Double-competitive failure assessment method based on pipe body strain and circumferential weld fracture toughness

Abstract

The invention belongs to the field of pipeline failure assessment, and relates to a double-competition failure assessment method based on pipe body strain and circumferential weld fracture toughness. According to the method, based on the high-grade steel pipeline containing the circumferential weld cracks under the action of the landslide, the J integral critical index of the circumferential weld material fracture toughness of the high-grade steel pipeline is determined through a three-point bending test, and a structural strain and fracture toughness calculation model of the high-grade steel pipeline containing the circumferential weld cracks under the action of the landslide is established; the method comprises the following steps: determining influence laws of pipeline, crack and landslide parameters on strain and J integral, respectively establishing pipe body strain and circumferential weld crack J integral prediction models by adopting particle swarm optimization (PSO) and a long short term memory neural network (LSTM) embedded algorithm (PSO-LSTM), and finally establishing a double-competition failure assessment method based on pipe body strain and circumferential weld fracture toughness. And a pipeline safety evaluation series atlas is formed. The landslide pipeline failure evaluation method integrating the pipe body strain and the circumferential weld fracture toughness is formed, the landslide pipeline double-competition failure evaluation method is optimized, the safety state of the landslide pipeline can be scientifically and accurately evaluated through field verification, and practicability is high.

Description

Technical Field

[0001] The invention belongs to the field of pipeline failure assessment and relates to a double-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 pipelines. Due to welding problems, various types of defects will inevitably appear on the girth welds, which will become the weak points of the pipelines. At the same time, high-grade steel long-distance pipelines often pass through mountainous areas prone to landslides. The presence of crack defects in the girth welds of the pipelines under the action of landslide loads will make the pipelines more prone to failure. Therefore, it is urgent to establish a method that can scientifically and accurately assess the risk of landslide pipelines.

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

[0004] The mechanical research on pipelines under landslides mainly focuses on the force application method, pipeline mechanical response and factor analysis. Liao et al. simplified the landslide action by using the strength reduction method, and studied the influence of different influencing factors on the J-integral of the circumferential crack through ABAQUS finite element simulation. Banushi et al. and Zahid et al. established finite element models of buried pipelines laid on transverse slopes under landslides, and analyzed the influence of different influencing factors on pipeline stress and strain. At present, most scholars use yield strength as the failure indicator of pipelines, but high-grade steel pipelines have good ductility, and the failure indicator of stress exceeding yield strength will cause a waste of material strength, so a strain-based failure indicator should be used.

[0005] At present, most of the research is about the complete pipeline under the action of landslide, and does not involve the crack of the girth weld. At the same time, for the safety evaluation of pipelines with crack defects, most of them are currently carried out by only one method, and the evaluation process is relatively simple. Therefore, the present invention takes the high-grade steel pipeline with girth weld crack under the action of landslide as the object, establishes a dual competitive failure evaluation method based on pipe body strain and girth weld fracture toughness, and forms a series of pipeline safety evaluation 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 in the above background, the present invention proposes a dual-competition failure evaluation 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 pipeline, the critical index of the fracture toughness J integral of the girth weld material is determined through a three-point bending test;

[0009] S102: Considering the nonlinear discontinuous landslide effect between landslide and pipeline, a calculation model for the structural strain and fracture toughness of high-grade steel pipelines with circumferential weld cracks under landslide 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 body strain distribution and the girth weld crack J-integral simulation results, the PSO-LSTM neural network is used to establish the pipe body strain and girth weld crack J-integral prediction models respectively;

[0011] 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 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 circumferential weld crack under landslide 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: 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 the action of a landslide.

[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 simulation results of pipe body strain and girth weld crack J-integral 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 of landslide pipeline based on the dual competition of 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] —Tensile limit strain, %; λ T —Yield strength ratio; ξ—Ratio of defect length to pipe wall thickness; η—Ratio of defect height to wall thickness;

[0021] S402: Calculate the pipe body strain and the girth weld crack J-integral through 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.

[0022] S403: Calculate the pipe body strain and its allowable strain and the J-integral of the circumferential weld crack under different pipeline, crack and landslide characteristic parameters to form a series of pipeline safety evaluation graphs. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic flow chart of a dual-competition failure assessment method based on pipe body strain and girth weld fracture toughness of the present invention;

[0024] Figure 2 It is the PSO-LSTM neural network framework of the present invention;

[0025] Figure 3 The comparison result between the predicted value and the simulated value of the pipe body strain of the present invention;

[0026] 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;

[0027] Figure 5 This is the pipeline safety evaluation map of the present invention. DETAILED DESCRIPTION

[0028] 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:

[0029] Step 1: Based on the girth weld of a 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.

[0030] Step 2: 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;

[0031] The interaction between the landslide and the pipeline takes into account the nonlinear discontinuous dynamic effects;

[0032] 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 the action of a landslide.

[0033] Step 3: Establish the J-integral prediction model of pipe body strain and girth weld crack;

[0034] The PSO algorithm is used to optimize the initial hyperparameters in the LSTM neural network module to form a PSO-LSTM neural network algorithm;

[0035] The simulation results of pipe body strain and girth weld crack J-integral under different pipeline, crack and landslide characteristic parameters are divided into training set and test set respectively. The prediction models of pipe body strain and girth weld crack J-integral are established by using PSO-LSTM neural network algorithm through the training set. The accuracy of the prediction model is verified by 20 test sets. The comparison results of pipe body strain prediction value and simulation value are shown in Figure 3 The fitting degree between the simulated value and the predicted value is greater than 0.98, indicating that the prediction model has high accuracy; the predicted value and the simulated value of the J-integral prediction model for the 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.

[0036] Step 4: Establish a landslide pipeline failure assessment method based on the dual competition of pipe body strain and girth weld fracture toughness;

[0037] The allowable strain of the pipe body is calculated by formula (1):

[0038] —Tensile limit strain, %; λ T —Yield strength ratio; ξ—Ratio of defect length to pipe wall thickness; η—Ratio of defect height to wall thickness;

[0039] The pipe body strain and the J-integral of the girth weld crack are calculated through 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 the 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.

[0040] Calculate the pipe body strain and its allowable strain and the J integral of the circumferential 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 of ​​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, the safety status of the pipeline under a certain landslide size can be evaluated.

[0041] The parameters of a landslide pipeline and its risks are shown in Table 1. According to the pipeline and crack parameters, the ultimate strain region of the main body is closer to the origin, so the safety evaluation should be carried out according to the pipe body strain evaluation method. The landslide parameters in Table 1 are within the ultimate strain region of the main body. Therefore, according to the pipeline safety evaluation map established by the present invention, the landslide pipeline has no risk.

[0042] 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, a dual competitive 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.

[0043] Table 1 Landslide pipeline parameters and their risks

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 (Figure 1): S101: Based on the girth weld of high-grade steel pipeline, the critical index of the fracture toughness J integral of the girth weld material is determined through a three-point bending test; S102: Considering the nonlinear discontinuous landslide effect between landslide and pipeline, a calculation model for the structural strain and fracture toughness of high-grade steel pipelines with circumferential weld cracks under landslide 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 body strain distribution and the girth weld crack J-integral simulation results, the PSO-LSTM neural network is used to establish the pipe body 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 pipe body strain and girth weld fracture toughness J-integral failure criterion, forming a series of pipeline safety evaluation maps under different pipeline, crack and landslide characteristic parameters.

2. The dual competitive failure assessment method based on pipe body strain and girth weld fracture toughness as described in claim 1 is characterized in that: The calculation model of strain and fracture toughness of high-grade steel pipeline structure with circumferential weld crack under landslide is established: 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 the action of a landslide.

3. The dual competitive failure assessment method based on pipe body strain and girth weld fracture toughness as described in 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 simulation results of pipe body strain and girth weld crack J-integral 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 as described in 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: —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; S402: Calculate the pipe body strain and the girth weld crack J-integral through 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 circumferential weld crack under different pipeline, crack and landslide characteristic parameters to form a series of pipeline safety evaluation graphs.

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