Method and system for safety assessment of girth welds of pipes containing misaligned defects under bending loads

Abstract

The present application relates to the technical field of oil and gas pipeline weld detection, and particularly relates to a method and system for safety evaluation of a pipeline girth weld with misaligned defects under bending load, which comprises: constructing an analytical approximate expression of the maximum equivalent stress on the pipeline girth weld with misaligned defects under the action of internal pressure and bending load, and correcting the expression by using a finite element model to obtain a calculation expression, and then calculating the equivalent stress of the girth weld with misaligned defects under the action of internal pressure and bending load, when the equivalent stress does not exceed a preset equivalent stress threshold, it is determined that the girth weld with misaligned defects is safe, and when the equivalent stress exceeds the preset equivalent stress threshold, it is determined that the girth weld with misaligned defects is unsafe, solving the problem of accurate stress calculation of the local complex detail position of the weld of the large-scale overall pipeline under the action of bending load, and improving the calculation accuracy and efficiency of the detail stress of the girth weld.

Description

Technical Field

[0001] This invention relates to the field of weld inspection technology for oil and gas pipelines, and in particular to a method and system for safety assessment of circumferential welds with misalignment defects in pipelines under bending loads. Background Technology

[0002] In recent years, cases of circumferential weld failures in oil and gas pipelines have occurred frequently, with some failures causing significant casualties and economic losses, and triggering panic. Circumferential weld failures are mainly caused by three factors: the weld's inherent mechanical properties, weld defects, and external loads. According to accident investigation reports and failure analysis reports, external loads other than internal pressure, especially bending loads caused by geological disasters such as landslides, are one of the important factors leading to circumferential weld failures. Various defects may occur during the welding process of pipeline circumferential welds, such as porosity, misalignment, slag inclusions, incomplete penetration, lack of fusion, and cracks. Compared to harmful defects such as cracks, misalignment is a more common welding defect with a higher frequency of occurrence. (See [link to relevant documentation]). Figure 1 Misalignment defects cause discontinuities in the weld structure, preventing a smooth transition with the base material and easily leading to localized stress concentrations, which seriously affects the service safety of circumferential welds. For more serious defects such as incomplete penetration, lack of fusion, and cracks, replacement of the pipe is usually addressed after detection. Misalignment defects, however, are typically prevented and controlled using stress monitoring and other methods.

[0003] To ensure the structural safety of circumferential welds, determining the extent of stress and strain caused by external loads beyond the design pressure during monitoring has become a key focus and challenge in pipeline integrity management. This is a core issue in pipeline stress and strain detection and early warning systems. Existing safety assessment methods for circumferential welds with misalignment defects calculate additional stress using the net section bending moment when additional bending loads are present. However, in practical applications, the bending moment on the circumferential weld is often undetermined, making direct evaluation impossible. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to address the shortcomings of the prior art by providing a method and system for safety assessment of circumferential welds of pipes with misalignment defects under bending loads.

[0005] The technical solution of the present invention for a safety assessment method of a pipe circumferential weld with misalignment defects under bending load is as follows: An analytical approximate expression for the maximum equivalent stress on the circumferential weld of a pipe with misalignment defects under internal pressure and bending load is constructed. A finite element model was established using the finite element method to calculate the effective stress of a circumferential weld seam containing misalignment defects in a pipe under internal pressure and bending loads. Based on the finite element model, the analytical approximate expression of the maximum equivalent stress is modified to obtain the calculation expression of the maximum equivalent stress on the circumferential weld of the pipe with misalignment defects under internal pressure and bending load. Acquire and input the basic information of the steel pipes on both sides of the circumferential weld with misalignment defects to be evaluated, as well as the misalignment amount, pipe slippage displacement or pipe deformation deflection and pipe span of the circumferential weld with misalignment defects to be evaluated, into the calculation expression, and calculate the equivalent stress of the circumferential weld with misalignment defects to be evaluated under internal pressure and bending load. When the equivalent stress does not exceed the preset equivalent stress threshold, the circumferential weld with misaligned edge defect to be evaluated is determined to be safe; when the equivalent stress exceeds the preset equivalent stress threshold, the circumferential weld with misaligned edge defect to be evaluated is determined to be unsafe.

[0006] The technical solution of the safety assessment system for pipe circumferential welds with misalignment defects under bending load according to the present invention is as follows: It includes a construction module, an establishment module, a correction module, a calculation module, and an evaluation module; The construction module is used to: construct an analytical approximate expression for the maximum equivalent stress on the circumferential weld of a pipe with misalignment defects under internal pressure and bending load; The establishment module is used to: establish a finite element model for calculating the effective stress of a pipe circumferential weld with misalignment defects under internal pressure and bending load using the finite element method; The correction module is used to: based on the finite element model, correct the analytical approximate expression of the maximum equivalent stress, and obtain the calculation expression of the maximum equivalent stress on the circumferential weld of the pipe with misalignment defects under the action of internal pressure and bending load; The calculation module is used to: acquire and input the basic information of the steel pipes on both sides of the circumferential weld with misalignment defects to be evaluated, as well as the misalignment amount, pipe slip displacement or pipe deformation deflection and pipe span of the circumferential weld with misalignment defects to be evaluated, input the calculation expression, and calculate the equivalent stress of the circumferential weld with misalignment defects to be evaluated under internal pressure and bending load. The evaluation module is used to: determine that the circumferential weld with misaligned edge defects to be evaluated is safe when the equivalent stress does not exceed a preset equivalent stress threshold, and determine that the circumferential weld with misaligned edge defects to be evaluated is unsafe when the equivalent stress exceeds the preset equivalent stress threshold.

[0007] The beneficial effects of this invention are: The influence of bending loads on the strength of circumferential welds in pipelines with misalignment defects was considered. In particular, the pipeline deformation deflection was introduced into the calculation formula, allowing the critical stress of the circumferential weld to be calculated using deflection. This solves the problem of not being able to directly obtain the bending moment on the pipeline in existing evaluation methods, making it more operable. Simultaneously, in the finite element model, the use of a sub-modeling and analysis method solves the problem of accurately calculating the stress at complex local details of the weld in large-scale overall pipelines under bending loads, improving the accuracy and efficiency of calculating the detailed stress of the circumferential weld. Attached Figure Description

[0008] Other features, objects, and advantages of the invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a schematic diagram of a circumferential weld with misalignment defects. Figure 2 This is a flowchart illustrating a method for safety assessment of a pipe circumferential weld with misalignment defects under bending load, according to an embodiment of the present invention. Figure 3 A schematic diagram of a circumferential weld with misalignment defects subjected to internal pressure and bending loads; Figure 4 This is a schematic diagram of a safety assessment system for a pipe circumferential weld with misalignment defects under bending load, according to an embodiment of the present invention. Detailed Implementation

[0009] like Figure 2 As shown in the figure, a method for safety assessment of a pipe circumferential weld with misalignment defects under bending load according to an embodiment of the present invention includes the following steps: S1. Construct an analytical approximate expression for the maximum equivalent stress on a circumferential weld of a pipe with misalignment defects under internal pressure and bending loads. The structure of the circumferential weld of the pipe with misalignment defects under internal pressure and bending loads is as follows: Figure 3 As shown; S2. Using the finite element method, establish a finite element model for calculating the effective stress of the circumferential weld of a pipe with misalignment defects under internal pressure and bending load; S3. Based on the finite element model, the analytical approximation expression for the maximum equivalent stress is corrected, and the undetermined coefficients in the analytical approximation expression are solved using the finite element calculation results and a data fitting method. A 1 ~A 5 and undetermined functions g(e, f) To achieve the correction, we obtain the calculation expression for the maximum equivalent stress on the circumferential weld of a pipe with misalignment defects under internal pressure and bending load; S4. Obtain and input the basic information of the steel pipes on both sides of the circumferential weld with misalignment defects to be evaluated, as well as the misalignment amount of the circumferential weld with misalignment defects to be evaluated, the pipe slippage displacement or pipe deformation deflection and the pipe span, and input the calculation expression to calculate the equivalent stress of the circumferential weld with misalignment defects to be evaluated under internal pressure and bending load. S5. When the equivalent stress does not exceed the preset equivalent stress threshold, the circumferential weld with misaligned edge defects to be evaluated is determined to be safe. When the equivalent stress exceeds the preset equivalent stress threshold, the circumferential weld with misaligned edge defects to be evaluated is determined to be unsafe.

[0010] Optionally, in the above technical solution, the basic information of the steel pipes on both sides of the circumferential weld with misalignment defects to be evaluated includes: outer diameter of the steel pipe, wall thickness, pipeline design pressure, elastic modulus of the steel pipe material, and Poisson's ratio.

[0011] Optionally, in the above technical solution, the analytical approximation expression is: in, Indicates the outer diameter of the steel pipe, Indicates wall thickness, Indicates the pipeline design pressure, Indicates the elastic modulus of steel pipe material, Represents Poisson's ratio. Indicates the amount of misalignment, This indicates pipeline landslide displacement or pipeline deformation deflection. Indicates the pipe span. r This indicates the inner radius of the steel pipe.

[0012] Optionally, in the above technical solution, the calculation expression is: R represents the outer radius of the steel pipe.

[0013] Optionally, in the above technical solution, the basic information of the steel pipes on both sides of the circumferential weld with misalignment defects to be evaluated also includes: yield strength and tensile strength, with a preset equivalent stress threshold of [missing information]. in , σ'=1 / 2(σ s +s b ), among which,p s Indicates yield strength, s b Indicates tensile strength.

[0014] The purpose of this invention is to overcome the shortcomings of existing safety assessment methods for circumferential welds with misalignment defects. Specifically, for pipelines in disaster-prone areas where landslides or subsidence may occur, this invention provides a safety assessment method for circumferential welds with misalignment defects under bending loads. This method can assess the safety of circumferential welds with misalignment defects by measuring pipeline landslide displacement or pipeline deformation deflection. In the formula, the bending load is expressed as a function of deflection. f This method demonstrates that the stress of the circumferential weld of a pipeline under bending loads corresponding to pipeline landslide displacement or pipeline deformation deflection can be obtained. The safety of the circumferential weld of a pipeline with misalignment defects can be determined by analyzing the stress. Specifically, this includes: S11. Obtain basic information about the steel pipes on both sides of the circumferential weld with misalignment defects to be evaluated, specifically including the outer diameter of the steel pipes. D Wall thickness t Pipeline design pressure P Elastic modulus of steel pipe material E Poisson's ratio m Yield strength s s ,tensile strength s b ; S12. Obtain the misalignment amount of the circumferential weld containing misalignment defects to be evaluated. e、 Pipeline landslide displacement or pipeline deformation deflection f and pipeline span l The misalignment amount 'e' is measured using a welding inspection ruler, while the landslide displacement or pipeline deformation deflection is provided by on-site inspection personnel.

[0015] S13. Through theoretical analysis and formula derivation, an analytical approximate expression for calculating the maximum equivalent stress on the circumferential weld of a pipe with misalignment defects under internal pressure and bending load is obtained: S14. Based on S11 and S12, a finite element model for stress calculation of circumferential weld seams with misalignment defects in pipelines under internal pressure and bending loads is established using the finite element method. The finite element model adopts the conventional sub-model modeling method in ABAQUS software, as detailed below: S140. Perform overall modeling, modeling the pipe and circumferential weld together at full size according to the span, diameter, and thickness. Due to the regular shape, the mesh can be relatively sparse. In the overall model, the size of the circumferential weld is very small compared to the large-span pipe, and its impact on the overall model result is limited. Therefore, the circumferential weld modeling can be ignored in the overall model. S141. Model the circumferential weld and its surrounding area in the sub-model. This step involves precise geometric modeling of the circumferential weld. Due to the small size of the sub-model, the mesh can be made relatively dense, thus enabling high-precision analysis of the circumferential weld.

[0016] S142. After finite element calculation using ABAQUS software, the sub-model boundary condition definition method of ABAQUS can be used to automatically extract the nodal displacements in the overall global model finite element results and apply them as boundary conditions to the sub-model boundary to reproduce the stress state of the sub-model in the overall model.

[0017] S15. Based on the stress results obtained from the finite element calculation in S14, the undetermined coefficients in the analytical approximation expression are obtained using data fitting methods and data analysis software. A 1 ~A 5 and undetermined functions g(e, f) This leads to a fitting correction, resulting in the expression for calculating the maximum equivalent stress on the circumferential weld of a pipe with misalignment defects under internal pressure and bending loads: S16. Calculate the critical stress, i.e. the preset equivalent stress threshold, of the circumferential weld seam of a pipe with misalignment defects using the following formula: σ'=1 / 2(σ s + s b ） S17. Substituting the pipe parameters, circumferential weld misalignment, pipe span, and deformation deflection into the above calculation expression, we obtain the equivalent stress σ of the circumferential weld with misalignment defects under internal pressure and bending loads. Then: 1) When s<s' If the condition is met, the circumferential weld with misalignment defects to be evaluated is deemed safe, meaning that the circumferential weld can be safely put into service under the current condition. 2) When in the If the defect is found, the circumferential weld containing misalignment is deemed unsafe and cannot continue to be used; appropriate measures must be taken.

[0018] Taking a section of the West-East Gas Pipeline II with a potential geological disaster at its circumferential weld seam as an example, the pipeline specifications are D1219mm×18.4mm, X80 steel grade, and the pipeline design pressure is 12MPa. During the investigation of potential hazards at the circumferential weld seam, a misalignment defect was found at a certain location, with a maximum misalignment of 5mm. The steps are as follows: (1) Obtain basic information about the steel pipes on both sides of the circumferential weld with misalignment defects to be evaluated, specifically including the outer diameter of the steel pipes. D Wall thickness t Pipeline design pressure P Elastic modulus of steel pipe material E Poisson's ratio m Yield strength s s,tensile strength s b ; outer diameter of the pipe to be evaluated D It is 1219mm, inner radius r It is 591.1 mm thick. t The pipe is 18.4mm thick, made of X80 material with a density of 7.8g / cm³. 3 The elastic modulus is 210,000 MPa, Poisson's ratio is 0.3, and the yield strength is... s s 555MPa, tensile strength s b It is 625 MPa.

[0019] (2) Obtain the misalignment amount of the circumferential weld containing misalignment defects to be evaluated. e Pipeline landslide displacement or pipeline deformation deflection f and pipeline span l .

[0020] Misalignment of circumferential weld with misalignment defects to be evaluated e The pipe deformation deflection is 5mm. f The span of the pipeline where the landslide occurred is 1000mm. l It is 20m.

[0021] (3) Based on steps (1) and (2), through theoretical analysis and formula derivation, an analytical approximate expression for calculating the maximum equivalent stress on the circumferential weld of a pipe with misalignment defects under internal pressure and bending load is obtained: (4) Based on steps (1) and (2), a finite element model for stress calculation of the circumferential weld of a pipe with misalignment defects under internal pressure and bending load is established using the finite element method. The finite element model adopts the conventional sub-model modeling method in ABAQUS software. Basic idea: 1) Perform overall modeling, modeling the pipe and circumferential weld at full size according to the span, diameter, and thickness. Due to the regular shape, the mesh can be relatively sparse. In the overall model, the size of the circumferential weld is very small compared to the large-span pipe, and its impact on the overall model result is limited. Therefore, the circumferential weld modeling can be ignored in the overall model. 2) Modeling the circumferential weld and its surrounding area in the sub-model: This step involves precise geometric modeling of the circumferential weld. Due to the small size of the sub-model, the mesh can be made relatively dense, thus enabling high-precision analysis of the circumferential weld.

[0022] 3) Extract the nodal displacements from the global model finite element results and apply them as boundary conditions to the sub-model boundary to reproduce the stress state of the sub-model in the global model.

[0023] (5) Based on the stress results obtained from the finite element calculation in step (4), the undetermined coefficients in the analytical approximate expression are obtained by using data fitting method through data analysis software. A1~A5 and undetermined functions g(e, f) This leads to a fitting correction, resulting in the expression for calculating the maximum equivalent stress on the circumferential weld of a pipe with misalignment defects under internal pressure and bending loads: (6) Calculate the critical stress of the circumferential weld of the pipeline with misalignment defects, i.e., the preset equivalent stress threshold, using the following formula: σ'=1 / 2(σ s +s b )=590MPa (7) Substitute the parameters from steps (1) and (2) into the equivalent stress calculation expression to obtain the equivalent stress of the circumferential weld of the pipe with misalignment defects under internal pressure and bending load. s We can obtain: σ=474MPa<σ' (8) The evaluation shows that the circumferential weld can be safely used under the current condition, and the stress of the circumferential weld can be monitored in real time.

[0024] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a safety assessment method for circumferential welds of pipelines with misalignment defects under bending loads. This method considers the influence of bending loads on the strength of circumferential welds with misalignment defects, particularly by incorporating pipeline deformation deflection into the calculation formula. f By incorporating bending loads into the formula for calculating the maximum equivalent stress of circumferential welds in pipelines with misalignment defects, the critical stress of the circumferential weld can be calculated using deflection. This solves the problem of not being able to directly obtain the bending moment on the pipeline in existing evaluation methods, making it more operable. Furthermore, in the finite element model, the use of a sub-modeling and analysis method solves the problem of accurately calculating the stress at complex local details of the weld in large-scale overall pipelines under bending loads, improving the accuracy and efficiency of calculating detailed stresses in circumferential welds.

[0025] In the above embodiments, although the steps are numbered S1, S2, etc., they are only specific embodiments given in this application. Those skilled in the art can adjust the execution order of S1, S2, etc. according to the actual situation, which is also within the protection scope of this invention. It can be understood that in some embodiments, some or all of the above embodiments may be included.

[0026] like Figure 4As shown, an embodiment of the present invention provides a safety assessment system 200 for a pipe circumferential weld with misalignment defects under bending load, comprising a construction module 210, an establishment module 220, a correction module 230, a calculation module 240, and an evaluation module 250. Module 210 is used to: construct an analytical approximate expression for the maximum equivalent stress on a circumferential weld of a pipe with misalignment defects under internal pressure and bending loads; Module 220 is used to: establish a finite element model for calculating the effective stress of a pipe circumferential weld with misalignment defects under internal pressure and bending loads using the finite element method; The correction module 230 is used to: correct the analytical approximate expression of the maximum equivalent stress based on the finite element model, and obtain the calculation expression of the maximum equivalent stress on the circumferential weld of the pipe with misalignment defects under internal pressure and bending load; The calculation module 240 is used to: acquire and input the basic information of the steel pipes on both sides of the circumferential weld with misalignment defects to be evaluated, as well as the misalignment amount of the circumferential weld with misalignment defects to be evaluated, the pipe slip displacement or pipe deformation deflection and the pipe span, input the calculation expression, and calculate the equivalent stress of the circumferential weld with misalignment defects to be evaluated under internal pressure and bending load. The evaluation module 250 is used to: determine that the circumferential weld with misaligned edge defects to be evaluated is safe when the equivalent stress does not exceed the preset equivalent stress threshold, and determine that the circumferential weld with misaligned edge defects to be evaluated is unsafe when the equivalent stress exceeds the preset equivalent stress threshold.

[0027] Optionally, in the above technical solution, the basic information of the steel pipes on both sides of the circumferential weld with misalignment defects to be evaluated includes: outer diameter of the steel pipe, wall thickness, pipeline design pressure, elastic modulus of the steel pipe material, and Poisson's ratio.

[0028] Optionally, in the above technical solution, the analytical approximation expression is: in, Indicates the outer diameter of the steel pipe, Indicates wall thickness, Indicates the pipeline design pressure, Indicates the elastic modulus of steel pipe material, Represents Poisson's ratio. Indicates the amount of misalignment, This indicates pipeline landslide displacement or pipeline deformation deflection. Indicates the pipe span. r This indicates the inner radius of the steel pipe.

[0029] Optionally, in the above technical solution, the calculation expression is: R represents the outer radius of the steel pipe.

[0030] Optionally, in the above technical solution, the basic information of the steel pipes on both sides of the circumferential weld with misalignment defects to be evaluated also includes: yield strength and tensile strength, with a preset equivalent stress threshold of [missing information]. in , σ'=1 / 2(σ s +s b ), among which,p s Indicates yield strength, s b Indicates tensile strength.

[0031] The parameters and steps of each unit module in the above-described safety assessment system 200 for pipe circumferential welds with misalignment defects under bending load of the present invention can be referred to the parameters and steps in the embodiments of the method for safety assessment of pipe circumferential welds with misalignment defects under bending load described above, and will not be repeated here.

[0032] An electronic device according to an embodiment of the present invention includes a memory, a processor, and a program stored in the memory and running on the processor. When the processor executes the program, it implements the steps of a method for safety assessment of a pipe circumferential weld with misalignment defects under bending load as described above.

[0033] The electronic device can be a computer, mobile phone, etc., and the corresponding program is computer software or mobile APP, etc. The parameters and steps of the above-mentioned electronic device of the present invention can be referred to the parameters and steps in the embodiment of the method for safety assessment of pipe circumferential weld with misalignment defects under bending load in the above text, and will not be repeated here.

[0034] Those skilled in the art will know that this invention can be implemented as a system, method, or computer program product.

[0035] Therefore, this disclosure can be implemented in the following forms: it can be entirely hardware, entirely software (including firmware, resident software, microcode, etc.), or a combination of hardware and software, generally referred to herein as a "circuit," "module," or "system." Furthermore, in some embodiments, the invention can also be implemented as a computer program product in one or more computer-readable media containing computer-readable program code.

[0036] Any combination of one or more computer-readable media may be used. A computer-readable medium can be a computer-readable signal medium or a computer-readable storage medium. A computer-readable storage medium can be, for example, but not limited to, an electrical, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any combination thereof. More specific examples (a non-exhaustive list) of computer-readable storage media include: an electrical connection having one or more wires, a portable computer disk, a hard disk, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fiber, portable compact disk read-only memory (CD-ROM), optical storage device, magnetic storage device, or any suitable combination thereof. In this document, a computer-readable storage medium can be any tangible medium that contains or stores a program that can be used by or in connection with an instruction execution system, apparatus, or device.

[0037] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for safety assessment of circumferential welds of pipes with misalignment defects under bending load, characterized in that, include: An analytical approximate expression for the maximum equivalent stress on the circumferential weld of a pipe with misalignment defects under internal pressure and bending load is constructed. A finite element model was established using the finite element method to calculate the effective stress of a circumferential weld seam containing misalignment defects in a pipe under internal pressure and bending loads. Based on the finite element model, the analytical approximate expression of the maximum equivalent stress is modified to obtain the calculation expression of the maximum equivalent stress on the circumferential weld of the pipe with misalignment defects under internal pressure and bending load. Acquire and input the basic information of the steel pipes on both sides of the circumferential weld with misalignment defects to be evaluated, as well as the misalignment amount, pipe slippage displacement or pipe deformation deflection and pipe span of the circumferential weld with misalignment defects to be evaluated, into the calculation expression, and calculate the equivalent stress of the circumferential weld with misalignment defects to be evaluated under internal pressure and bending load. When the equivalent stress does not exceed the preset equivalent stress threshold, the circumferential weld with misaligned edge defect to be evaluated is determined to be safe; when the equivalent stress exceeds the preset equivalent stress threshold, the circumferential weld with misaligned edge defect to be evaluated is determined to be unsafe. The basic information of the steel pipes on both sides of the circumferential weld with misalignment defects to be evaluated includes: outer diameter of the steel pipe, wall thickness, pipeline design pressure, elastic modulus of the steel pipe material, and Poisson's ratio; The analytical approximation expression is: in, Indicates the outer diameter of the steel pipe, Indicates wall thickness, Indicates the pipeline design pressure, Indicates the elastic modulus of steel pipe material, Represents Poisson's ratio. Indicates the amount of misalignment, This indicates pipeline landslide displacement or pipeline deformation deflection. Indicates the pipe span. r Indicates the inner radius of the steel pipe; The calculation expression is: R represents the outer radius of the steel pipe.

2. The method for safety assessment of circumferential welds with misalignment defects in pipelines under bending loads according to claim 1, characterized in that, The basic information of the steel pipes on both sides of the circumferential weld with misalignment defects to be evaluated also includes: yield strength and tensile strength, and the preset equivalent stress threshold is... σ' , σ'=1 / 2(σ s +σ b ), where σ s Indicates yield strength, σ b Indicates tensile strength.

3. A safety assessment system for circumferential welds of pipes with misalignment defects under bending loads, characterized in that, It includes a construction module, an establishment module, a correction module, a calculation module, and an evaluation module; The construction module is used to: construct an analytical approximate expression for the maximum equivalent stress on the circumferential weld of a pipe with misalignment defects under internal pressure and bending load; The establishment module is used to: establish a finite element model for calculating the effective stress of a pipe circumferential weld with misalignment defects under internal pressure and bending load using the finite element method; The correction module is used to: based on the finite element model, correct the analytical approximate expression of the maximum equivalent stress, and obtain the calculation expression of the maximum equivalent stress on the circumferential weld of the pipe with misalignment defects under the action of internal pressure and bending load; The calculation module is used to: acquire and input the basic information of the steel pipes on both sides of the circumferential weld with misalignment defects to be evaluated, as well as the misalignment amount, pipe slip displacement or pipe deformation deflection and pipe span of the circumferential weld with misalignment defects to be evaluated, input the calculation expression, and calculate the equivalent stress of the circumferential weld with misalignment defects to be evaluated under internal pressure and bending load. The evaluation module is used to: determine that the circumferential weld with misaligned edge defects to be evaluated is safe when the equivalent stress does not exceed a preset equivalent stress threshold, and determine that the circumferential weld with misaligned edge defects to be evaluated is unsafe when the equivalent stress exceeds the preset equivalent stress threshold. The basic information of the steel pipes on both sides of the circumferential weld with misalignment defects to be evaluated includes: outer diameter of the steel pipe, wall thickness, pipeline design pressure, elastic modulus of the steel pipe material, and Poisson's ratio; The analytical approximation expression is: in, Indicates the outer diameter of the steel pipe, Indicates wall thickness, Indicates the pipeline design pressure, Indicates the elastic modulus of steel pipe material, Represents Poisson's ratio. Indicates the amount of misalignment, This indicates pipeline landslide displacement or pipeline deformation deflection. Indicates the pipe span. r Indicates the inner radius of the steel pipe; The calculation expression is: R represents the outer radius of the steel pipe.

4. The safety assessment system for pipe circumferential welds with misalignment defects under bending load as described in claim 3, characterized in that, The basic information of the steel pipes on both sides of the circumferential weld with misalignment defects to be evaluated also includes: yield strength and tensile strength, and the preset equivalent stress threshold is... σ' , σ'=1 / 2(σ s +σ b ), where σ s Indicates yield strength, σ b Indicates tensile strength.

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