A dual-competition failure assessment method based on pipe body strain and girth weld fracture toughness

Abstract

The present invention belongs to the field of pipeline failure assessment and relates to a dual-competition failure assessment method based on pipe body strain and girth weld fracture toughness. The present invention is based on a high-grade steel pipeline with girth weld cracks under the action of landslide. The critical index of the fracture toughness J-integral of the girth weld material of the high-grade steel pipeline is determined through a three-point bending test. A calculation model of the structural strain and fracture toughness of the high-grade steel pipeline with girth weld cracks under the action of landslide is established. The influence of pipeline, crack and landslide parameters on strain and J-integral is determined. The particle swarm optimization (PSO) and long short-term memory neural network (LSTM) mosaic algorithm (PSO-LSTM) are used to respectively establish pipe body strain and girth weld crack J-integral prediction models. Finally, a dual-competition failure assessment method based on pipe body strain and girth weld fracture toughness is established, and a series of pipeline safety evaluation maps are formed. The present invention forms a landslide pipeline failure assessment method integrating pipe body strain and girth weld fracture toughness, optimizes the dual-competition failure assessment method for landslide pipelines, and is field-verified to be able to scientifically and accurately assess the safety status of landslide pipelines, with strong practicality.

Description

Technical Field

[0001] The present invention belongs to the field of pipeline failure assessment and relates to a dual-competition failure assessment method based on pipe body strain and girth weld fracture toughness. Background Art

[0002] High-grade steel pipelines are widely used in long-distance transportation. Due to welding problems, various types of defects inevitably appear in the girth welds, which can become weak points in the pipelines. Furthermore, high-grade steel pipelines often pass through mountainous areas prone to landslides. The presence of cracks in the girth welds under landslide loads can increase the susceptibility of pipeline failure. Therefore, a method is urgently needed to scientifically and accurately assess the risk of pipeline landslides.

[0003] To date, mechanical research on crack-defective pipelines has primarily focused on safety assessments of crack-defective pipelines under specific loads and crack sizes, selecting specific evaluation index parameters. Jiang et al. used the ABAQUS finite element model to study the fracture response of defects in the butt weld of a miter-jointed X70 pipeline and the influence of related parameters on the crack driving force. Jacquemin et al. analyzed the effects of crack depth and weld misalignment position on the J-integral for cracks on the misaligned sides of pipeline welds. Shen et al. used ABAQUS software to study the effects of different influencing factors on cracks in the girth weld of an X80 pipeline, obtained the distribution of the J-integral at the crack tip, and established a strain-based failure assessment diagram.

[0004] Mechanical research on pipelines under landslides has primarily focused on force application methods, pipeline mechanical responses, and factor analysis. Liao et al. simplified the landslide effect using a strength reduction method and investigated the impact of various factors on the J-integral of circumferential cracks through ABAQUS finite element simulation. Banushi et al. and Zahid et al. established finite element models for buried pipelines laid on transverse slopes under landslides, analyzing the effects of various factors on pipeline stress and strain. Currently, most researchers use yield strength as a pipeline failure indicator. However, high-grade steel pipelines have good ductility, and failure indicators based on stress exceeding yield strength will result in a waste of material strength. Therefore, a strain-based failure indicator should be used.

[0005] Most current research focuses on intact pipelines exposed to landslides, not girth weld cracks. Furthermore, safety assessments for pipelines with crack defects often rely on a single method, resulting in a relatively simplistic evaluation process. Therefore, this paper examines high-grade steel pipelines exposed to landslides and containing girth weld cracks, establishing a dual-competition failure assessment method based on pipe strain and girth weld fracture toughness, and developing a series of pipeline safety assessment maps. Summary of the Invention

[0006] In order to solve the problem of safety evaluation of high-grade steel pipelines with girth weld cracks under landslide action in the above background, the present invention proposes a dual-competition failure assessment method based on pipe body strain and girth weld fracture toughness.

[0007] A dual-competition failure assessment method based on pipe body strain and girth weld fracture toughness mainly includes the following four steps:

[0008] S101: Based on the girth weld of high-grade steel pipelines, the critical index of the fracture toughness J integral of the girth weld material is determined through a three-point bend test;

[0009] S102: Considering the nonlinear discontinuous landslide effect between the landslide and the pipeline, a calculation model for the structural strain and fracture toughness of a high-grade steel pipeline with a circumferential weld crack under landslide action is established, and the pipe body strain and J-integral value under different pipeline, crack and landslide characteristic parameters are determined;

[0010] S103: Combining the pipe strain distribution and girth weld crack J-integral simulation results, a PSO-LSTM neural network is used to establish pipe strain and girth weld crack J-integral prediction models respectively;

[0011] S104: A pipeline landslide failure assessment method based on the dual competition of pipe body strain and girth weld fracture toughness is established by combining pipe body strain and fracture toughness J-integral failure criterion, forming a series of pipeline safety evaluation maps under different pipeline, crack and landslide characteristic parameters.

[0012] The calculation model of strain and fracture toughness of high-grade steel pipeline structure with girth weld crack under landslide action is established according to the following steps:

[0013] S201: The interaction between landslide and pipeline takes into account the nonlinear discontinuous dynamic effects;

[0014] S202: Couple the landslide-pipeline-weld-crack modules to establish a calculation model for the strain and fracture toughness of a high-grade steel pipeline structure with a circumferential weld crack under landslide action.

[0015] The strain and J-integral prediction model is determined by the following steps:

[0016] S301: Using the PSO algorithm to optimize the initial hyperparameters in the LSTM neural network module to form a PSO-LSTM neural network algorithm;

[0017] S302: Based on the pipe body strain and girth weld crack J-integral simulation results under different pipeline, crack and landslide characteristic parameters, the PSO-LSTM neural network algorithm is used to establish pipe body strain and girth weld crack J-integral prediction models respectively.

[0018] The failure assessment method for landslide pipelines based on the dual competition between pipe body strain and girth weld fracture toughness is implemented in the following steps:

[0019] S401: Calculate the allowable strain of the pipe body using formula (1).

[0020]

[0021] —Tensile ultimate strain, %; λ T —yield strength ratio; ξ—ratio of defect length to pipe wall thickness; η—ratio of defect height to wall thickness;

[0022] S402: Calculate the pipe body strain and the girth weld crack J-integral using the strain and J-integral prediction model. When the pipe body strain is less than the allowable strain or the girth weld J-integral is less than the critical fracture toughness J-integral value, the landslide pipeline fails. Therefore, a landslide pipeline failure assessment method based on the dual competition of pipe body strain and girth weld fracture toughness is established by combining the pipe body strain and girth weld fracture toughness J-integral failure criterion.

[0023] S403: Calculate the pipe body strain and its allowable strain and the J-integral of the girth weld crack under different pipeline, crack and landslide characteristic parameters to form a series of pipeline safety evaluation maps. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of a process of a dual-competition failure assessment method based on pipe body strain and girth weld fracture toughness according to the present invention;

[0025] Figure 2 It is the PSO-LSTM neural network framework of the present invention;

[0026] Figure 3 The comparison results between the predicted value and the simulated value of the pipe body strain of the present invention are as follows;

[0027] Figure 4 The predicted value and simulated value of the J-integral prediction model of the girth weld crack of the present invention and their relative errors;

[0028] Figure 5 This is the pipeline safety evaluation map of the present invention. DETAILED DESCRIPTION

[0029] A dual-competition failure assessment method based on pipe body strain and girth weld fracture toughness is described in detail through the following specific implementation methods:

[0030] Step 1: Based on the girth weld of high-grade steel pipeline, determine the critical index of the fracture toughness J integral of the girth weld material through a three-point bending test.

[0031] Step 2: Establish a calculation model for the strain and fracture toughness of a high-grade steel pipeline structure with a girth weld crack under landslide action;

[0032] The interaction between the landslide and the pipeline takes into account the nonlinear discontinuous dynamic effect;

[0033] The landslide-pipeline-weld-crack modules are coupled to establish a calculation model for the strain and fracture toughness of a high-grade steel pipeline structure with a circumferential weld crack under landslide action.

[0034] Step 3: Establish a J-integral prediction model for pipe body strain and girth weld crack;

[0035] The PSO algorithm is used to optimize the initial hyperparameters in the LSTM neural network module to form a PSO-LSTM neural network algorithm;

[0036] The J-integral simulation results of pipe strain and girth weld crack under different pipeline, crack and landslide characteristic parameters were divided into training set and test set respectively. The PSO-LSTM neural network algorithm was used to establish the pipe strain and girth weld crack J-integral prediction models respectively based on the training set. The accuracy of the prediction model was verified by 20 test sets. The comparison results of pipe strain prediction value and simulation value are shown in Fig. Figure 3 The fitting degree between the simulated value and the predicted value is greater than 0.98, indicating that the prediction model is highly accurate. The predicted value and the simulated value of the J-integral prediction model for girth weld crack and their relative errors are shown in Figure 4 , the maximum relative error is 9.59%, and the prediction model has high accuracy.

[0037] Step 4: Establish a failure assessment method for landslide pipelines based on the dual competition of pipe body strain and girth weld fracture toughness;

[0038] The allowable strain of the pipe body is calculated by formula (1):

[0039]

[0040] —Tensile ultimate strain, %; λ T —yield strength ratio; ξ—ratio of defect length to pipe wall thickness; η—ratio of defect height to wall thickness;

[0041] The pipe body strain and girth weld crack J-integral are calculated using the strain and J-integral prediction model. When the pipe body strain is less than the allowable strain or the girth weld J-integral is less than the critical fracture toughness J-integral value, the landslide pipeline fails. Combining the pipe body strain and girth weld fracture toughness J-integral failure criterion, a landslide pipeline failure assessment method based on the dual competition of pipe body strain and girth weld fracture toughness is established.

[0042] Calculate the pipe body strain and its allowable strain and the J integral of the girth weld crack under different pipeline, crack and landslide characteristic parameters to form the following Figure 5The pipeline safety evaluation map shown in the figure; the area below each color box (serial number) represents the safety area under the corresponding conditions, but because the map is based on the comprehensive safety evaluation of pipe body strain and girth weld crack fracture toughness, the final safety area should be the area closer to the origin of the two safety areas obtained based on the two evaluation methods; for pipelines and landslides with known structural dimensions, the pipeline safety evaluation map can obtain the maximum allowable crack size, or if the crack size contained in a specific pipeline structure is known, it can evaluate the safety status of the pipeline under a certain landslide size.

[0043] Table 1 shows the parameters and risks of a landslide pipeline. Based on the pipeline and crack parameters, the ultimate strain region of the pipeline itself is closer to the origin, so a safety assessment should be conducted based on the pipe strain evaluation method. The landslide parameters in Table 1 are within the ultimate strain region of the pipeline itself. Therefore, according to the pipeline safety evaluation map established by this invention, this pipeline presents no risk of landslide.

[0044] The actual measured equivalent stress of the landslide pipeline is 298 MPa, which does not exceed the yield strength of the pipeline. Therefore, the landslide pipeline is risk-free. At the same time, the dual-competition failure assessment method based on pipe body strain and girth weld fracture toughness established by the present invention can accurately reflect the safety status of the landslide pipeline.

[0045] Table 1 Landslide pipeline parameters and their risks

[0046]

Claims

1. A dual-competition failure assessment method based on pipe body strain and girth weld fracture toughness, characterized in that: The process includes the following: S101: Based on the girth weld of high-grade steel pipelines, the critical index of the fracture toughness J integral of the girth weld material is determined through a three-point bend test; S102: Considering the nonlinear discontinuous landslide effect between the landslide and the pipeline, a calculation model for the structural strain and fracture toughness of a high-grade steel pipeline with a circumferential weld crack under landslide action is established, and the pipe body strain and J-integral value under different pipeline, crack and landslide characteristic parameters are determined; S103: Combining the pipe strain distribution and girth weld crack J-integral simulation results, a PSO-LSTM neural network is used to establish pipe strain and girth weld crack J-integral prediction models respectively; S104: A landslide pipeline failure assessment method based on the dual competition of pipe body strain and girth weld fracture toughness is established by combining the J-integral failure criterion of pipe body strain and girth weld fracture toughness, forming a series of pipeline safety evaluation maps under different pipeline, crack and landslide characteristic parameters.

2. The dual-competition failure assessment method based on pipe body strain and girth weld fracture toughness according to claim 1 is characterized in that: Establish a calculation model for the strain and fracture toughness of a high-grade steel pipeline structure with a circumferential weld crack under landslide action: S201: The interaction between landslide and pipeline takes into account the nonlinear discontinuous dynamic effects; S202: Couple the landslide-pipeline-weld-crack module to establish a calculation model for the strain and fracture toughness of a high-grade steel pipeline structure with a circumferential weld crack under landslide action.

3. The dual competition failure assessment method based on pipe body strain and girth weld fracture toughness according to claim 1 is characterized in that: The PSO-LSTM neural network algorithm is used to establish strain and J-integral prediction models respectively: S301: Using the PSO algorithm to optimize the initial hyperparameters in the LSTM neural network module to form a PSO-LSTM neural network algorithm; S302: Based on the pipe body strain and girth weld crack J-integral simulation results under different pipeline, crack and landslide characteristic parameters, the PSO-LSTM neural network algorithm is used to establish pipe body strain and girth weld crack J-integral prediction models respectively.

4. The dual competition failure assessment method based on pipe body strain and girth weld fracture toughness according to claim 1 is characterized in that: A failure assessment method for landslide pipelines based on the dual competition between pipe body strain and girth weld fracture toughness was established: S401: The allowable strain of the pipe body is calculated by the following formula: Where: ε t crit —ultimate tensile strain, %; λ T —yield strength ratio; ξ—ratio of defect length to pipe wall thickness; η—ratio of defect height to wall thickness; S402: Calculate the pipe body strain and the girth weld crack J-integral using the strain and J-integral prediction model. When the pipe body strain is less than the allowable strain or the girth weld J-integral is less than the critical fracture toughness J-integral value, the landslide pipeline fails. Therefore, a landslide pipeline failure assessment method based on the dual competition of pipe body strain and girth weld fracture toughness is established by combining the pipe body strain and girth weld fracture toughness J-integral failure criterion. S403: Calculate the pipe body strain and its allowable strain and the J-integral of the girth weld crack under different pipeline, crack and landslide characteristic parameters to form a series of pipeline safety evaluation maps.

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