Pipeline corrosion defect evaluation method and device

Abstract

The present invention discloses a pipeline corrosion defect evaluation method, which at least comprises the following steps: obtaining pipeline parameters and defect parameters; obtaining the allowable stress [σ] of the pipeline; establishing a finite element model according to the obtained pipeline parameters and defect parameters; obtaining the maximum stress σ at the corrosion defect through simulation of the established finite element model. max ; Establish the pipeline corrosion defect evaluation equation A=[σ] / σ max , obtain the safe state of the pipeline, where A=[σ] / σ max >1, the pipeline is considered to be in a safe state; when A=[σ] / σ max When ≤1, the pipeline is considered to be in a failed state. The present invention also discloses a pipeline corrosion defect evaluation device. The pipeline corrosion defect evaluation method and device of the present invention avoid the conservatism of the existing formula, and the evaluation result is more accurate and has a wider scope of application.

Description

Technical Field

[0001] The invention relates to the technical field of petrochemical industry, and in particular to a pipeline corrosion defect evaluation method and device. Background Art

[0002] With the rapid development of the economy, the demand for energy transportation has increased. Among the many modes of transportation, pipeline transportation has developed rapidly around the world due to its advantages such as low cost, large transportation volume, high safety and stable supply. It plays an irreplaceable role in industries such as petrochemicals and natural gas transportation. With the increase of service life, pipeline corrosion has become more and more serious, the pressure bearing capacity of pipelines has decreased, and accidents such as perforation, leakage and rupture have occurred from time to time. Predicting and evaluating the corrosion defects of pipelines and taking precautions can reduce the safety risks of pipeline operation.

[0003] The residual strength evaluation of defective pipelines (also known as safety assessment) is based on pipeline defect detection. Through rigorous theoretical analysis, experimental testing and mechanical calculations, the maximum allowable operating pressure (MAOP) of the pipeline and the critical defect size of the current working pressure are determined, providing a basis for pipeline maintenance and replacement, as well as pressure increase and decrease operations.

[0004] Residual strength evaluation methods can generally be divided into four categories: (1) semi-empirical formulas obtained based on a large number of hydraulic burst tests on defective pipe sections; (2) analytical analysis methods based on elastic-plastic mechanics and fracture mechanics theory; (3) finite element numerical calculation methods; (4) based on the failure criteria of defective pipelines, combined with probability and reliability theory, to establish a probabilistic evaluation method for defective pipelines. At present, there are many evaluation methods and standard specifications in the world, such as ASME B31G, API579, DNV RP-F101, BS 7910, etc.

[0005] At present, the commonly used strength evaluation formulas in the world are mostly based on the NG-18 surface defect calculation formula of fracture mechanics. However, the formulas in the existing technology are all empirical and simplified to a certain extent, and cannot analyze specific defect conditions, such as the shape of the defect and material properties.

[0006] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention and should not be regarded as an acknowledgment or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art. Summary of the invention

[0007] One of the purposes of the present invention is to provide a pipeline corrosion defect evaluation method and device, thereby improving the problem that the evaluation formula in the prior art cannot accurately analyze the pipeline corrosion defects.

[0008] Another object of the present invention is to provide a pipeline corrosion defect evaluation method and device, so that the applicability is wider.

[0009] To achieve the above object, according to a first aspect of the present invention, a pipeline corrosion defect evaluation method is provided, which comprises at least the following steps: obtaining pipeline parameters and defect parameters; obtaining the allowable stress [σ] of the pipeline; establishing a finite element model according to the obtained pipeline parameters and defect parameters; obtaining the maximum stress σ at the corrosion defect through simulation of the established finite element model. max ; Establish the pipeline corrosion defect evaluation equation A=[σ] / σ max , obtain the safe state of the pipeline, where A=[σ] / σ max >1, the pipeline is considered to be in a safe state; when A=[σ] / σ max When ≤1, the pipeline is considered to be in a failed state.

[0010] Furthermore, in the above technical solution, the parameters of the pipeline include the material, outer diameter, wall thickness, maximum allowable working pressure, elastic modulus E, Poisson's ratio, yield stress σ s , tensile strength and safety factor F s .

[0011] Furthermore, in the above technical solution, the parameters of the defect include the length, depth and width of the defect.

[0012] Furthermore, in the above technical solution, in the step of establishing the finite element model, the stress-strain relationship of the material of the pipeline adopts the Ramberg-Osgood model: Where, the initial strain ε0 = σ s / E, α is the hardening coefficient; n is the power hardening exponent.

[0013] Furthermore, in the above technical solution, the step of establishing the finite element model includes the following assumptions: the material of the pipeline has a plastic stress-strain state and has geometric nonlinearity and material nonlinearity; the effect of the internal pressure on the inner wall of the pipeline is considered; for axial defects, the constraints and supports of the external environment on the pipeline are considered; and for circumferential defects, the effect of the external environment on the outer wall of the pipeline is ignored.

[0014] Furthermore, in the above technical solution, in the finite element model, the length of the pipeline is greater than or equal to three times the diameter.

[0015] Furthermore, in the above technical solution, in the finite element model, the two ends of the defect are 1 / 4 spheres, and the middle part is cylindrical.

[0016] Furthermore, in the above technical solution, a finite element model is established using a 20-node hexahedral isoparametric unit.

[0017] According to a second aspect of the present invention, the present invention provides a pipeline corrosion defect evaluation device, comprising: a parameter acquisition module, which is used to acquire pipeline parameters and defect parameters; a finite element model establishment module, which is used to establish a finite element model according to the acquired pipeline parameters and defect parameters; an evaluation module, which is used to establish a pipeline corrosion defect evaluation equation to obtain the safety status of the pipeline.

[0018] Furthermore, in the above technical solution, the parameters of the pipeline include the material, outer diameter, wall thickness, maximum allowable working pressure, elastic modulus E, Poisson's ratio, yield stress σ s , tensile strength and safety factor F s ;The parameters of the defect include the length and depth of the defect.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. The pipeline corrosion defect evaluation method and device of the present invention avoid the conservatism of existing formulas, and the evaluation results are more accurate.

[0021] 2. The pipeline corrosion defect evaluation method and device of the present invention can be simulated according to the parameters of different types of pipelines and defects, and has a wider scope of application than the prior art.

[0022] 3. When building the model, a 1 / 4 sphere is used as the defect end. The model is more consistent with the actual corrosion defect shape, rather than simplifying the defect into a cuboid, and the simulation results are more accurate.

[0023] 4. The acquisition of the residual strength of the corroded pipeline is closely related to the material parameters, defect morphology and pipeline size. The residual strength evaluation formulas in the existing standards are mostly fitted from the fracture mechanics formula NG-18, which is old. With the increase of pipeline steel grades, there are conservative problems. In addition, except for the standard DNV-RP-F101, complex corrosion defects are regarded as single defects; the material parameters are relatively few, and the elasticity and plasticity of pipeline steel cannot be reflected; for the convenience of engineering use, the defects are usually greatly simplified. The present invention uses finite element technology, and the experimental verification, material model and calculation model are more perfect. The finite element method can also easily and quickly solve traditional complex engineering problems quickly and accurately.

[0024] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, and to make the above and other purposes, technical features and advantages of the present invention easier to understand, one or more preferred embodiments are listed below and described in detail with the accompanying drawings as follows. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1It is a schematic flow chart of a pipeline corrosion defect evaluation method according to one embodiment of the present invention.

[0026] Figure 2 Schematic diagram of a finite element model of a pipeline corrosion defect evaluation method according to an embodiment of the present invention.

[0027] Figure 3 It is a finite element model simulation result of a pipeline corrosion defect evaluation method according to an embodiment of the present invention. DETAILED DESCRIPTION

[0028] The specific implementation modes of the present invention are described in detail below in conjunction with the accompanying drawings, but it should be understood that the protection scope of the present invention is not limited by the specific implementation modes.

[0029] Unless explicitly stated otherwise, throughout the specification and claims, the term “comprise” or variations such as “include” or “comprising”, etc., will be understood to include the stated elements or components but not to exclude other elements or components.

[0030] In this document, for the convenience of description, spatial relative terms such as "below", "below", "down", "above", "above", "upper", etc. may be used to describe the relationship between one element or feature and another element or feature in the accompanying drawings. It should be understood that the spatial relative terms are intended to include different orientations of the object in use or operation in addition to the orientation depicted in the figure. For example, if the object in the figure is turned over, the element described as being "below" or "below" other elements or features will be oriented "above" the element or feature. Therefore, the exemplary term "below" can include both the below and above directions. Objects may also have other orientations (rotated 90 degrees or other orientations) and the spatial relative terms used in this document should be interpreted accordingly.

[0031] In this document, the terms "first", "second", etc. are used to distinguish two different elements or parts, and are not used to limit a specific position or relative relationship. In other words, in some embodiments, the terms "first", "second", etc. can also be interchangeable.

[0032] like Figure 1 As shown, according to a specific embodiment of the present invention, the pipeline corrosion defect evaluation method comprises at least the following steps: obtaining pipeline parameters and defect parameters; obtaining the allowable stress [σ] of the pipeline; establishing a finite element model according to the obtained pipeline parameters and defect parameters; obtaining the maximum stress σ at the corrosion defect through simulation of the established finite element model. max ; Establish the pipeline corrosion defect evaluation equation A=[σ] / σ max , obtain the safe state of the pipeline, where A=[σ] / σ max>1, the pipeline is considered to be in a safe state; when A=[σ] / σ max When ≤1, the pipeline is considered to be in a failed state.

[0033] In engineering, allowable stress [σ] is used as the maximum stress that a part or structure can withstand. When the working stress in the structure does not exceed the allowable stress, the structure is considered safe in operation. Otherwise, it is unsafe or called failure. The allowable stress is equal to the failure stress appropriately corrected after considering various influencing factors divided by the safety factor. s is the limit, because when the stress value is greater than the yield stress of the material, the material cannot maintain its original shape and size, so it is considered that safe operation cannot be guaranteed. Yield stress divided by safety factor F s Then the allowable stress is obtained, that is, [σ] = σ s / F s The design coefficient can be obtained from the design specifications during the pipeline design and construction phase.

[0034] In one or more embodiments of the present invention, a pipeline corrosion defect evaluation device according to a specific embodiment of the present invention includes: a parameter acquisition module, which is used to acquire pipeline parameters and defect parameters; a finite element model establishment module, which is used to establish a finite element model according to the acquired pipeline parameters and defect parameters; an evaluation module, which is used to establish a pipeline corrosion defect evaluation equation to obtain the safety status of the pipeline.

[0035] Example 1

[0036] In this embodiment, the pipeline corrosion defect evaluation method of the present invention is used to analyze the actual oil and gas pipeline of a certain project. The parameters of the pipeline (material, outer diameter, wall thickness, maximum allowable operating pressure MAOP, elastic modulus E, Poisson's ratio, yield stress σ s , tensile strength and safety factor F s ) are shown in the following table.

[0037]

[0038] Allowable stress [σ] = σ s / F s =320 / 2=160MPa.

[0039] In this embodiment, the length of the pipeline corrosion defect is 30 mm, the depth is 30% of the wall thickness, and the width is 5.7 mm. Many documents show that the axial defect has a greater impact on pressure, while the annular width has a smaller impact. This embodiment uses the axial defect for simulation.

[0040] According to the characteristics of oil and gas pipelines, the finite element model of the pipeline is established with the following assumptions: the material of the pipeline has a plastic stress-strain state and has geometric nonlinearity and material nonlinearity; the effect of internal pressure on the inner wall of the pipeline is considered; for axial defects, the constraints and supports of the external environment on the pipeline are considered; and for circumferential defects, the effect of the external environment on the outer wall of the pipeline is ignored.

[0041] In the step of establishing the finite element model, the stress-strain relationship of the pipeline material adopts the Ramberg-Osgood model: Where, the initial strain ε0 = σ s / E, α is the hardening coefficient; n is the power hardening exponent. Through experimental verification, this model has a good representation of the elastic-plastic properties of the material.

[0042] like Figure 2 As shown in the figure, in order to eliminate the influence of the model end on the simulation, in the established finite element model, the length of the pipe is equal to three times the diameter; the two ends of the defect are 1 / 4 spheres, and the middle part is cylindrical. The finite element model is established using a 20-node hexahedral isoparametric unit, and according to the symmetry of the problem, 1 / 2 of the pipe body with axial defects is taken.

[0043] Boundary conditions are added according to the actual constraints of the pipeline. The sections at both ends of the axial direction are fixed, that is, the displacement and rotation in the X, Y, and Z directions are all 0; symmetric boundary conditions are added to the annular interface, and the plane perpendicular to the X-axis, the displacement in the X direction is 0, and it cannot rotate about the Y and Z axes; fixed constraints are added to the bottom of the pipeline, that is, the rotational displacement in the X, Y, and Z directions is zero, to simulate the support constraint of the soil.

[0044] The simulation results of this embodiment are as follows Figure 3 As shown in the figure, according to the simulation results, the maximum stress σ at the corrosion defect can be obtained. max =144.2MPa. Pipeline corrosion defect evaluation equation:

[0045] A=[σ] / σ max =160 / 144.2=1.11>1.

[0046] Therefore, it is considered that the pipeline in this embodiment is in a safe state and does not need to be repaired immediately, but it still needs to be continuously observed and tested.

[0047] The foregoing description of specific exemplary embodiments of the present invention is for the purpose of illustration and demonstration. These descriptions are not intended to limit the present invention to the precise form disclosed, and it is clear that many changes and variations can be made based on the above teachings. The purpose of selecting and describing the exemplary embodiments is to explain the specific principles of the present invention and its practical application, so that those skilled in the art can realize and utilize various different exemplary embodiments of the present invention and various different selections and changes. Any simple modifications, equivalent changes and modifications made to the above exemplary embodiments should fall within the scope of protection of the present invention.

Claims

1. A pipeline corrosion defect evaluation method, characterized in that: At least the following steps are included: Obtain the parameters of the pipeline and the parameters of the defect; the parameters of the pipeline include the material, outer diameter, wall thickness, maximum allowable working pressure, elastic modulus E, Poisson's ratio, yield stress σ of the pipeline s , tensile strength and safety factor F s ; The parameters of the defect include the length, depth and width of the defect; Obtaining the allowable stress [σ] of the pipeline; A finite element model is established based on the acquired parameters of the pipeline and the parameters of the defects; the steps of establishing the finite element model include the following assumptions: the material of the pipeline has a plastic stress-strain state and has geometric nonlinearity and material nonlinearity; the effect of internal pressure on the inner wall of the pipeline is considered; For axial defects, the constraints and supports of the external environment on the pipe are considered; and for circumferential defects, the effects of the external environment on the outer wall of the pipe are ignored; Through the established finite element model simulation, the maximum stress σ at the corrosion defect is obtained. max ; Establish the pipeline corrosion defect evaluation equation A=[σ] / σ max , get the pipeline's security status, Among them, when A=[σ] / σ max When >1, the pipeline is considered to be in a safe state; When A=[σ] / σ max When ≤1, the pipeline is considered to be in a failed state.

2. The pipeline corrosion defect evaluation method according to claim 1, characterized in that: In the step of establishing the finite element model, the stress-strain relationship of the material of the pipeline adopts the Ramberg-Osgood model: Where, the initial strain ε0 = σ s / E, α is the hardening coefficient; n is the power hardening exponent; ε is the actual strain, σ is the actual stress, σ s is the yield stress.

3. The pipeline corrosion defect evaluation method according to claim 1, characterized in that: In the finite element model, the length of the pipe is greater than or equal to three times of its diameter.

4. The pipeline corrosion defect evaluation method according to claim 1, characterized in that: In the finite element model, the two ends of the defect are 1 / 4 spheres, and the middle part is cylindrical.

5. The pipeline corrosion defect evaluation method according to claim 1, characterized in that: The finite element model was established using 20-node hexahedral isoparametric elements.

6. A pipeline corrosion defect evaluation device, characterized in that: Applying the method as claimed in any one of claims 1 to 5, comprising: A parameter acquisition module, which is used to obtain pipeline parameters and defect parameters; A finite element model building module, which is used to build a finite element model according to the acquired pipeline parameters and defect parameters; The evaluation module is used to establish the pipeline corrosion defect evaluation equation and obtain the safety status of the pipeline.

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