Mechanical-electrochemical effect sensitivity analysis method under internal and external defects of pipeline surface

Abstract

The invention belongs to the technical field of pipeline mechanical-electrochemical effect analysis, and relates to a mechanical-electrochemical effect sensitivity analysis method under internal and external defects on the surface of a pipeline. Based on a high-steel-grade pipeline with corrosion defects on the inner surface and the outer surface, a mechanical-electrochemical multi-physics field coupling model is built according to pipeline mechanical property parameters and neutral environment electrochemical parameters, and a mechanical-electrochemical multi-physics field coupling finite element model under the corrosion defects on the inner surface and the outer surface of the pipeline is built; by changing the depth and length of the corrosion defect, the relative position of the internal and external defects and the internal pressure of the pipeline, the sensitivity analysis of the mechanical-electrochemical interaction of the pipeline is carried out. According to the method, the mechanical-electrochemical interaction under the internal and external corrosion defects of the pipeline surface can be calculated, and the safety state of the mechanical-electrochemical interaction under the internal and external corrosion defects of the pipeline surface can be scientifically and accurately evaluated.

Description

Technical Field

[0001] The invention belongs to the technical field of pipeline mechanical-electrochemical effect analysis, and relates to a mechanical-electrochemical effect sensitivity analysis method under internal and external defects on the pipeline surface. Background Art

[0002] Submarine pipeline transportation is the most economical and efficient way to transport submarine oil and gas resources. However, due to the complex and changeable marine environment, the surface of submarine pipelines is prone to electrochemical corrosion and corrosion defects. Local corrosion defects can cause permanent plastic deformation and local strong stress concentration in the cross section of the pipeline. In addition, as a pressurized device, the complex stress and electrochemical reaction at the defect will produce a synergistic effect, thereby causing stress corrosion, which will have a significant impact on the safety of the pipeline. If the pipeline leaks, it will cause serious environmental pollution and economic losses. Therefore, it is very important to evaluate the mechanical-electrochemical interaction of internal and external defects on the pipeline surface in order to reduce the risk of pipeline failure.

[0003] So far, many scholars have conducted research on the mechanical-electrochemical interaction of pipeline defects. Xu and Cheng et al. conducted the first research on the mechanical-electrochemical interaction of pipeline defects, established a mechanical-electrochemical mathematical model under NS4 solution, and used COMSOL software to establish a pipeline defect model. The mechanical-electrochemical interaction at the defect was studied by changing the depth and tensile strain of the ellipsoidal corrosion defect. Sun et al. conducted a mechanical-electrochemical interaction of corrosion defects under different internal pressures of the pipeline based on X46 steel pipes containing adjacent circumferentially symmetrical corrosion defects. Yi et al. took the X100 steel pipe elbow with external corrosion defects as the research object, and studied the effects of different elbow radii, defect depths, internal pressures and pipe materials on the mechanical-electrochemical interaction.

[0004] Under the condition that defects exist both inside and outside the pipeline, Wang et al. used ANSYS software to study the stress distribution of the pipeline and the critical distance of the interaction between defects when defects exist on both the inner and outer surfaces of the pipeline. Guo et al. studied the diffusion and distribution of hydrogen atoms at the internal and external corrosion defects of X52 steel pipes under various longitudinal tensile strain conditions.

[0005] At present, there is a lack of results on the mechanical-electrochemical interaction under the presence of corrosion defects on both the inner and outer surfaces of the pipeline, resulting in the immaturity of the sensitivity analysis method of the mechanical-electrochemical interaction under this condition. Therefore, the present invention establishes a mechanical-electrochemical multi-physical field coupling finite element model under the internal and external corrosion defects on the pipeline surface, and carries out sensitivity analysis of the mechanical-electrochemical interaction of the pipeline under different corrosion defect depths and lengths, relative positions of internal and external defects and internal pressure of the pipeline, so as to propose a sensitivity analysis method of the mechanical-electrochemical effect under internal and external defects on the pipeline surface. Summary of the invention

[0006] In order to solve the problems described in the above background, the present invention proposes a method for analyzing the sensitivity of the mechanical-electrochemical effect to internal and external defects on the pipeline surface.

[0007] The sensitivity analysis method of mechanical-electrochemical effects under internal and external defects on the pipeline surface mainly includes the following four steps:

[0008] S101: Collect the mechanical properties parameters of high-grade steel pipelines and the electrochemical parameters of neutral environment;

[0009] S102: Couple pipeline mechanical performance parameters with neutral environment electrochemical parameters to build a mechanical-electrochemical multi-physics field coupling model.

[0010] Where: i c —Local cathode current density, A / m 2 ;i 0,c —Exchange current density, 3.46×10 -5 A / m 2 ; σ e —vonMises stress, MPa; V m —Molar volume of steel, 7.13×10 -6 m 2 / mol; F—Faraday constant, 96485.34C / mol; b c —Tafel slope, -0.09 V;

[0011] S103: Based on the actual geometric parameters and boundary conditions of the pipeline, a mechanical-electrochemical multi-physics field coupling finite element model is established under the internal and external corrosion defects of the pipeline surface;

[0012] S104: The sensitivity analysis of pipeline mechanical-electrochemical interaction is performed by changing the depth and length of corrosion defects, the relative positions of internal and external defects, and the internal pressure of the pipeline.

[0013] The established mechanical-electrochemical multi-physics field coupling model was obtained through semi-mechanistic and semi-empirical derivation and was used to describe the oxygen absorption reaction.

[0014] The mechanical-electrochemical multi-physics field coupling finite element model under internal and external corrosion defects on the pipeline surface is a two-dimensional model. The pipeline geometry model is established through the pipe diameter, wall thickness and pipe length. The corrosion defect shape is semi-elliptical, the boundaries at both ends of the pipeline are fixed constraints, and the inner surface boundary of the pipeline is a uniform internal pressure. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic flow chart of the method for analyzing the sensitivity of the mechanical-electrochemical effect to internal and external defects on the pipeline surface of the present invention;

[0016] Figure 2 It is the stress distribution curve of the inner and outer surfaces of the pipeline at different corrosion defect depths;

[0017] Figure 3 It is the distribution curve of anode current density on the inner and outer surfaces of the pipeline at different corrosion defect depths;

[0018] Figure 4 It is the stress distribution curve of the inner and outer surfaces of the pipeline under different corrosion defect lengths;

[0019] Figure 5 The anode current density distribution curve of the inner and outer surfaces of the pipeline under different corrosion defect lengths;

[0020] Figure 6 It is the stress distribution curve of the inner and outer surfaces of the pipeline under different relative positions of corrosion defects;

[0021] Figure 7 The distribution curve of anode current density on the inner and outer surfaces of the pipeline at different relative positions of corrosion defects;

[0022] Figure 8 It is the stress distribution curve of inner and outer surfaces of pipeline under different internal pressures;

[0023] Fig. 9 This is the distribution curve of anode current density on the inner and outer surfaces of the pipeline under different internal pressures. DETAILED DESCRIPTION

[0024] like Figure 1 As shown, the mechanical-electrochemical effect sensitivity analysis method under internal and external defects on the pipeline surface is described in detail through the following specific implementation methods:

[0025] Step 1: Collect the mechanical properties parameters of high-grade steel pipelines and the electrochemical parameters of neutral environment. The mechanical properties parameters and electrochemical parameters are shown in Table 1 and Table 2, respectively.

[0026] Table 1 Mechanical properties parameters of high-grade steel pipelines Steel Yield strength(MPa) Young's modulus(GPa) Poisson's ratio Ultimate tensile strength (MPa) X100 805 202 0.3 890

[0027] Table 2 Electrochemical parameters in neutral environment

[0028] Step 2: Couple the pipeline mechanical performance parameters with the neutral environment electrochemical parameters, and derive the mechanical-electrochemical multi-physics field coupling model describing the oxygen absorption reaction in a semi-mechanistic-semi-empirical way.

[0029] Where: i c —Local cathode current density, A / m2 ;i 0,c —Exchange current density, 3.46×10 -5 A / m 2 ; σ e —vonMises stress, MPa; V m —Molar volume of steel, 7.13×10 -6 m 2 / mol; F—Faraday constant, 96485.34C / mol; b c —Tafel slope, -0.09V.

[0030] Step 3: The pipeline geometry model is established through the pipe diameter, wall thickness and pipe length. The corrosion defect shape is set to a semi-ellipse. The boundaries at both ends of the pipeline are fixed constraints, and the inner surface boundary of the pipeline is a uniform internal pressure. Based on the above geometry and boundary conditions, a two-dimensional finite element model of mechanical-electrochemical multi-physical field coupling under internal and external corrosion defects on the pipeline surface is established.

[0031] Step 4: By changing the depth and length of the corrosion defect, the relative position of the internal and external defects and the internal pressure of the pipeline, the pipeline mechanical-electrochemical interaction sensitivity analysis is carried out. The sensitivity analysis model parameter settings are shown in Table 3.

[0032] Table 3. Sensitivity analysis model parameter settings Serial number Defect depth (mm) Defect length (mm) Defect offset (mm) Pipeline internal pressure (MPa) 1 6 / 4 20 / 20 0 10 2 4 / 4 20 / 20 0 10 3 2 / 4 20 / 20 0 10 4 4 / 4 30 / 20 0 10 5 4 / 4 20 / 20 0 10 6 4 / 4 10 / 20 0 10 7 4 / 4 20 / 20 -20 10 8 4 / 4 20 / 20 -15 10 9 4 / 4 20 / 20 -10 10 10 4 / 4 20 / 10 0 8 11 4 / 4 20 / 10 0 10 12 4 / 4 20 / 10 0 12

[0033] Through the above method of the present invention, the mechanical-electrochemical interaction sensitivity analysis can be performed on high-grade steel pipelines with corrosion defects on both the inner and outer surfaces of the pipeline, the sensitivity of the mechanical-electrochemical interaction of the pipeline with corrosion defects on both the inner and outer surfaces of the pipeline can be understood, the stress corrosion state of the pipeline can be determined, the safety state of the pipeline can be evaluated, and data support can be provided for the formulation of pipeline safety management measures.

Claims

1. A method for analyzing the sensitivity of mechanical-electrochemical effects to internal and external defects on the pipeline surface, characterized in that: The process includes the following: S101: Collect the mechanical properties parameters of high-grade steel pipelines and the electrochemical parameters of neutral environment; S102: Couple pipeline mechanical performance parameters with neutral environment electrochemical parameters to build a mechanical-electrochemical multi-physics field coupling model. Where: i c —Local cathode current density, A / m 2 ; i 0,c —Exchange current density, 3.46×10 -5 A / m 2 ; σ e —vonMises stress, MPa; V m —Molar volume of steel, 7.13×10 -6 m 2 / mol; F—Faraday constant, 96485.34C / mol; b c —Tafel slope, -0.09 V; S103: Based on the actual geometric parameters and boundary conditions of the pipeline, a mechanical-electrochemical multi-physics field coupling finite element model is established under the internal and external corrosion defects of the pipeline surface; S104: The sensitivity analysis of pipeline mechanical-electrochemical interaction is performed by changing the depth and length of corrosion defects, the relative positions of internal and external defects, and the internal pressure of the pipeline.

2. The method for analyzing the sensitivity of the mechanical-electrochemical effect to internal and external defects on the pipeline surface according to claim 1, characterized in that: The established mechanical-electrochemical multi-physics field coupling model was obtained through semi-mechanistic and semi-empirical derivation and was used to describe the oxygen absorption reaction.

3. The method for analyzing the sensitivity of the mechanical-electrochemical effect to internal and external defects on the pipeline surface according to claim 1, characterized in that: The mechanical-electrochemical multi-physics field coupling finite element model under internal and external corrosion defects on the pipeline surface is a two-dimensional model. The pipeline geometry model is established through the pipe diameter, wall thickness and pipe length. The corrosion defect shape is semi-elliptical, the boundaries at both ends of the pipeline are fixed constraints, and the inner surface boundary of the pipeline is a uniform internal pressure.

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