Prediction method for tensile deformation capacity of in-service pipeline
Through the combination of pipeline tensile test and finite element analysis model, the problem of difficulty in evaluating the tensile strain capacity of in-service pipelines is solved, and the rapid assessment and safety warning of pipeline strain capacity are achieved, providing a basis for geological disaster management.
Patent Information
- Application Number
- CN202311111700.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2023-08-30
- Publication Date
- 2025-02-28
AI Technical Summary
It is difficult for the prior art to accurately evaluate the tensile resilience capacity of in-service pipelines, especially in areas with frequent geological disasters. The deformation capacity of pipelines cannot be effectively predicted, resulting in an increase in safety risks.
The tensile stress-strain relationship was obtained through the pipeline tensile test, and a finite element analysis model of ring welds containing defects was established. A fracture driving force data database was established based on material properties and load conditions, and a multi-mesh interpolation method was used to predict and evaluate the tensile strain ability.
It has achieved a rapid assessment of the tensile strain capacity of in-service pipelines and ring welded joints, provided safety warnings, and provided goals and basis for geological disaster management.
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Figure CN119538621A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of deformation / fracture assessment of oil and gas transmission pipelines, and relates to a method for predicting the tensile deformation capacity of an in-service pipeline. Background Art
[0002] In general, pipeline failure is load-controlled failure, and the design criteria based on stress limit are adopted. However, for pipelines laid in areas prone to geological disasters such as earthquakes, debris flows, landslides, permafrost zones and seabeds, the load size cannot be controlled, and the deformation will only stop when the displacement reaches a certain level. At this time, the load is controlled by displacement or strain. In this case, the design based on stress limit criteria alone can no longer guarantee the safety of the pipeline. The strain limit criteria must be adopted, that is, the design strain of the pipeline must be less than the deformation capacity of the pipeline. This is the strain-based design concept of the pipeline, which is often used in the design of pipelines serving in earthquake, permafrost, ocean and other environments. For pipelines based on strain design, it is often required that the girth weld has high strength matching and high toughness (complete ductile behavior, or the upper platform of ductile-brittle transition at service temperature). On this basis, the fracture driving force of the girth weld when the maximum allowable defect is present and the tensile deformation is calculated, and the fracture resistance (fracture toughness or tear resistance curve) is compared to evaluate and predict the tensile strain capacity.
[0003] The strain capacity of pipelines is related to the geometric factors of pipeline steel pipes, such as the outer diameter and wall thickness of the pipe body, and the misalignment of the girth weld, and to the material properties, such as the strength of the pipe body and weld, deformation strengthening index, fracture toughness, etc. In engineering, the far-end strain of the pipeline when the defective girth weld reaches the tensile failure limit is generally used as the tensile strain capacity of the pipeline.
[0004] In recent years, due to the risk of geological disasters, strain-induced failures have also occurred in in-service pipelines. This requires quantitative evaluation of the tensile strain capacity of in-service pipelines to provide safety warnings when pipelines are deformed and provide targets and basis for geological disaster management. Since there are generally no requirements for strain-based design for in-service pipelines, there are often a large number of low-strength matching girth welds, and the fracture toughness does not meet the requirements for strain-based design, making it impossible to accurately evaluate the tensile strain capacity of in-service pipelines. Summary of the invention
[0005] In view of the problems existing in the prior art, the present invention provides a method for predicting the tensile deformation capacity of an in-service pipeline. By combining geometric parameters, tensile properties and fracture toughness parameters with service conditions, the evaluation value of the tensile strain capacity of the in-service pipeline and girth weld joint can be quickly determined.
[0006] The present invention is achieved through the following technical solutions:
[0007] A method for predicting the tensile deformation capacity of an in-service pipeline, comprising:
[0008] Through pipeline tensile test, the tensile stress-strain relationship of different regions of pipeline and girth weld is obtained, so as to obtain the tensile properties of different regions of pipeline;
[0009] Establishing a girth weld finite element analysis model containing defects according to relevant parameters of the pipeline and the girth weld joint; the girth weld finite element analysis model contains a maximum allowable defect;
[0010] By introducing the tensile properties of different regions of the pipeline into the finite element analysis model of the girth weld with defects, and then analyzing the finite element analysis model of the girth weld with defects, tensile deformation is applied to the pipeline in the analysis to obtain the fracture driving force information during the crack propagation process;
[0011] Based on the fracture driving force information and combined with the different levels of fracture toughness indexes of pipeline girth welds, a database of tensile strain capacity under different conditions of pipeline geometric characteristics and material properties is obtained;
[0012] According to the tensile strain capacity database, the tensile strain capacity of pipelines under different parameter conditions is predicted and evaluated by multivariate grid interpolation method.
[0013] Preferably, the specific process of obtaining the tensile properties of the pipeline is:
[0014] A longitudinal sample is taken from the pipeline, and the engineering stress-strain curve of the pipeline is obtained through a tensile test, and the tensile stress-strain relationship of the pipeline is obtained, thereby obtaining the tensile properties of the pipeline; the specifications of the longitudinal sample are a gauge width of 38.1 mm and a gauge length of 50.8 mm.
[0015] Preferably, the specific process of establishing the finite element analysis model of the girth weld with defects is:
[0016] Select multiple representative values for each parameter of the relevant parameters of the pipeline and the girth weld joint, combine the representative values of each wall thickness combination between girth weld joints with different wall thicknesses, and jointly establish a finite element analysis model of the girth weld with defects;
[0017] The relevant parameters of the pipeline and girth weld joint include performance parameters, geometric characteristics and defect parameters of the pipeline and girth weld;
[0018] The performance parameters of the pipeline and girth weld joint include the apparent toughness of the pipeline and girth weld, the strength and matching relationship of the pipe body and weld metal, and the softening degree of the heat-affected zone;
[0019] The geometrical features of the pipeline and the girth weld include the outer diameter of the pipeline, the wall thickness of the pipeline, the misalignment amount of the girth weld and the defect size. The wall thickness of the pipeline includes the unequal wall thickness of the girth weld joint.
[0020] Preferably, the defect dimensions include cap width, cap weld height, root weld height, root weld width, HAZ width and groove angle.
[0021] Preferably, the specific process of obtaining the fracture driving force information during crack propagation is:
[0022] According to the defects, load level and material properties of the pipeline, a tensile deformation analysis was performed on the finite element model of the defective girth weld. In the analysis, axial tensile deformation was applied to the pipeline to obtain the crack tip opening displacement data of the pipeline weld defect and its relationship with the tensile strain of the pipeline, thereby obtaining the characterization of the girth weld fracture driving force. By setting the ordinate to the fracture driving force expressed by the crack tip opening displacement and the abscissa to the tensile strain of the pipeline, the pipeline weld fracture driving force curve information during the crack propagation process was obtained.
[0023] Preferably, the load level includes the internal pressure borne by the pipeline, and the material properties include the yield strength, tensile strength and heat-affected zone softening degree of the pipeline.
[0024] Preferably, the fracture toughness index value of the material is obtained by characterizing the apparent toughness of the weld metal under different conditions.
[0025] Preferably, the pipeline weld fracture driving force data and the material fracture toughness index value are combined, and the pipeline tensile strain capacity data are obtained through the intersection value between the fracture driving force curve of the pipeline weld under different parameter conditions and the apparent toughness.
[0026] Preferably, according to the multivariate grid interpolation method, the specific process of evaluating and predicting the tensile strain capacity of pipelines under different parameter conditions is as follows:
[0027] The results of the tensile strain capacity of the pipeline are interpolated by linear grids through the specific working condition parameters of the pipeline, and then the relevant parameters of the pipeline and the girth weld joint are normalized. The relevant parameters of the normalized pipeline and the girth weld joint are combined with the linear grid interpolation to construct a multivariate linear interpolation function for strain capacity calculation in the grid space. The specific formula is:
[0028] TSC=F(f p ,ξ,α,η,δ A ,λ)
[0029] Among them, δA represents the fracture toughness level, λ represents the softening degree of the heat affected zone, and f p is the pressure coefficient of the pipeline, ξ is the yield strength ratio of the pipeline base material, α is the normalized unequal wall thickness difference, η is the normalized misalignment; TSC is the strain capacity;
[0030] The specific working condition parameters of the pipeline include pipeline wall thickness, apparent toughness, girth weld misalignment, heat affected zone softening degree, weld metal matching degree and internal pressure parameters.
[0031] Preferably, the normalized parameters of the pipeline and girth weld joint include:
[0032] The pressure coefficient of the pipe is f p =P d D / 2t min σ y ;
[0033] The yield strength ratio of the pipe base material is ξ=σ y / σ b ;
[0034] The difference in wall thickness of the girth weld joint is α=(t max -t min ) / t min ;
[0035] The misalignment of the girth weld is η = Δ / t min ;
[0036] Among them, f p is the pressure coefficient of the pipeline, P d is the operating pressure of the pipeline, D is the diameter of the pipeline, t min is the minimum wall thickness of the girth weld, t max is the maximum wall thickness of the girth weld joint, ξ is the yield strength ratio of the pipe base material, σ y is the yield strength of the pipe base material, σ b is the tensile strength of the pipe base material, α is the normalized unequal wall thickness difference, η is the normalized misalignment, and Δ is the misalignment.
[0037] Compared with the prior art, the present invention has the following beneficial technical effects:
[0038] The present invention provides a method for predicting the tensile deformation capacity of an in-service pipeline. The engineering stress-strain curve of the pipeline is obtained through a pipeline tensile test, and the tensile strain of the pipeline is obtained; a girth weld finite element analysis model is established according to relevant parameters of the pipeline and the girth weld joint; a fracture driving force data information library is established through the girth weld finite element analysis model and the tensile strain of the pipeline, combined with the material properties and loads of the pipeline; according to the fracture driving force data information library, combined with the fracture toughness index of the pipeline material, the data of tensile strain capacity under different pipeline and girth weld joint geometries and material performance conditions are obtained; according to the data of tensile strain capacity under each calculation condition, the tensile strain capacity of the pipeline under different parameter conditions is predicted and evaluated by a multivariate grid interpolation method. The present invention relates to simulating in-service pipelines and girth weld joints of specific specifications under actual service load conditions, subjected to tensile, bending and other loads and deformed, and determining the strain limit before the pipeline fails. The present invention finds the connection between pipeline-related geometry, performance, load parameters and tensile strain capacity. Through such a connection, the evaluation value of the tensile strain capacity of the in-service pipeline can be obtained, thereby providing an effective safety warning for the in-service pipeline and providing a goal and basis for the governance of geological disaster areas. Through geometric parameters, tensile properties and fracture toughness parameters, combined with service conditions, the evaluation value of the tensile strain capacity of the in-service pipeline and girth weld joint can be quickly determined. BRIEF DESCRIPTION OF THE DRAWINGS
[0039] Figure 1 A flow chart for predicting the tensile strain capacity of in-service pipelines;
[0040] Figure 2 It is a characterization diagram of the measurement parameters of the girth welding joint shape in the embodiment;
[0041] Figure 3 To establish a finite element calculation model diagram in the embodiment;
[0042] Figure 4 The tensile strain capacity is calculated according to the fracture toughness index in the embodiment;
[0043] Figure 5 The TSC with a wall thickness of 18.4 mm + 18.4 mm girth weld in the embodiment;
[0044] Figure 6 The TSC with a girth weld of 12.8 mm + 15.3 mm in wall thickness in the embodiment;
[0045] Figure 7 The TSC with a wall thickness of 12.8 mm + 12.8 mm girth weld in the embodiment;
[0046] Figure 8 The TSC with a wall thickness of 12.8mm+18.4mm girth weld in the embodiment. DETAILED DESCRIPTION
[0047] The present invention is further described in detail below in conjunction with specific embodiments, which are intended to explain the present invention rather than to limit it.
[0048] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.
[0049] A method for predicting the tensile deformation capacity of in-service pipelines, such as Figure 1 As shown, including,
[0050] The engineering stress-strain curve of the pipeline is obtained through the pipeline tensile test, and the tensile stress-strain curves of the materials in different regions of the pipeline are obtained, thereby obtaining the tensile properties of different regions of the pipeline;
[0051] A girth weld finite element analysis model is established according to relevant parameters of the pipeline and the girth weld joint; the girth weld finite element analysis model includes a maximum allowable defect. Since process defects are inevitable in welding structures, it is assumed that the weld has a maximum size defect allowed by the standard. In order to ensure the conservatism of the prediction results, a girth weld finite element analysis model including the maximum allowable defect needs to be established;
[0052] Through the finite element analysis model of the girth weld with the maximum allowable defect of the tensile properties of different regions such as the pipe body, weld metal, and heat affected zone, the finite element analysis model of the girth weld with defects is analyzed.
[0053] Based on the fracture driving force data information and the fracture toughness index value of the pipeline material, a database of tensile strain capacity under each calculation condition is obtained;
[0054] According to the database of tensile strain capacity under each calculation condition, the tensile strain capacity of the pipeline under different parameter conditions is predicted and evaluated by the multivariate grid interpolation method.
[0055] Furthermore, a longitudinal sample was taken from the pipeline, and an engineering stress-strain curve was obtained through a tensile test; the specification of the longitudinal sample was a gauge width of 38.1 mm and a gauge length of 50.8 mm;
[0056] Furthermore, the specific process of establishing the finite element analysis model of the girth weld is as follows:
[0057] Select multiple horizontal representative values for each parameter of the girth weld joint, combine the representative values of each wall thickness combination of girth weld joints with different wall thicknesses, and jointly establish a girth weld finite element analysis model;
[0058] The relevant parameters of the pipeline and girth weld joint include the performance, geometric characteristics, defect parameters of the pipeline and girth weld,
[0059] The performance parameters of the pipeline and girth weld joint include the apparent toughness of the pipeline and girth weld, the strength and matching relationship of the pipe body and weld metal, and the softening degree of the heat affected zone;
[0060] The geometrical characteristics of the pipeline and the girth weld include the outer diameter of the pipeline, the wall thickness of the pipeline (including the relationship of unequal wall thickness of the girth weld joint), the apparent toughness, the misalignment of the girth weld, the defect size and the weld metal matching.
[0061] Further, the defect size parameters include cap width, cap weld height, root weld height, root weld width, HAZ width and groove angle;
[0062] For girth welds of girth welds with unequal wall thickness, a 20° angle is added on the thicker side of the girth weld to characterize the inner groove, and an inner surface crack defect is introduced, and the crack tip is located on the fusion line between the heat-affected zone on the thinner side of the girth weld and the weld metal.
[0063] Further, the specific process of establishing the girth weld fracture driving force data information database is as follows:
[0064] According to the load level and material properties of the pipeline, through the finite element analysis model of the girth weld and the tensile strain of the pipeline, through the finite element simulation analysis, the opening displacement value of the crack tip of the pipeline weld and the distal strain of the girth weld joints with unequal wall thickness are recorded, and the driving force curve characterized by the girth weld fracture driving force is obtained, where the ordinate is the fracture driving force expressed by the opening displacement of the crack tip, and the abscissa is the tensile strain of the pipeline. The data of the pipeline weld fracture driving force under different working conditions are obtained, and the obtained data of the pipeline weld fracture driving force are sorted, recorded and stored to establish a fracture driving force data information database.
[0065] Furthermore, the load level includes the internal pressure borne by the pipeline, and the material properties include the yield strength, tensile strength and heat-affected zone softening degree of the pipeline.
[0066] Furthermore, the fracture toughness index value of the material is characterized by the apparent toughness of the weld metal under different conditions; the apparent toughness is obtained by assuming a typical value in combination with the test data of the corresponding welding process;
[0067] Furthermore, the pipeline weld fracture driving force data and the material fracture toughness index value are combined, and the pipeline tensile strain capacity data are obtained through the intersection value between the curve of pipeline weld fracture driving force under different parameter conditions and the apparent toughness.
[0068] Furthermore, according to the multivariate grid interpolation method, the specific process of evaluating and predicting the tensile strain capacity of pipelines under different parameter conditions is as follows:
[0069] The results of the tensile strain capacity of the pipeline are interpolated linearly through the specific working condition parameters of the pipeline. The multivariate linear interpolation function for strain capacity calculation is constructed in the grid space by combining the relevant parameters of the normalized pipeline and girth weld joint. The specific formula is:
[0070] TSC=F(fp,ξ,α,η,δA,λ)
[0071] Among them, δA represents the fracture toughness level, λ represents the softening degree of the heat-affected zone, fp is the pressure coefficient of the pipeline, ξ is the yield strength ratio of the pipeline base material, α is the normalized unequal wall thickness difference, and η is the normalized misalignment amount;
[0072] The specific working condition parameters of the pipeline include pipeline wall thickness, apparent toughness, girth weld misalignment, HAZ softening, weld metal matching and internal pressure parameters.
[0073] Furthermore, the normalized parameters of the pipe and girth weld joint include:
[0074] The pressure coefficient of the pipe is fp = PdD / 2tminσy;
[0075] The yield strength ratio of the pipe base material is ξ=σy / σb;
[0076] The difference in unequal wall thickness of the girth weld joint is α = (tmax-tmin) / tmin;
[0077] The misalignment of the girth weld is η = Δ / tmin;
[0078] Among them, fp is the pressure coefficient of the pipeline, Pd is the operating pressure of the pipeline, D is the pipeline diameter, tmin is the minimum wall thickness of the girth weld joint, tmax is the maximum wall thickness of the girth weld joint, ξ is the yield strength ratio of the pipeline base material, σy is the yield strength of the pipeline base material, σb is the tensile strength of the pipeline base material, α is the normalized unequal wall thickness difference, η is the normalized misalignment, and Δ is the misalignment.
[0079] HAZ stands for Heat-Affected Zone, which is the area between the metal substrate and the welding or heating area during welding or heat treatment. HAZ width refers to the width of the heat-affected zone, that is, the range of changes in the structure and properties of the metal substrate during welding or heating.
[0080] Example 1
[0081] Tube geometry
[0082] According to the specific on-site information of the in-service pipeline, the outer diameter is 1016mm, and the wall thickness is 12.8mm, 15.3mm, and 18.4mm. There are mainly two combinations of unequal wall thicknesses: 12.8mm and 15.3mm, and 12.8mm and 18.4mm. Therefore, there is one pipe diameter condition, and the wall thickness combination conditions of the girth weld joint are 12.8mm-12.8mm, 18.4mm-18.4mm, 12.8mm-15.3mm, and 12.8mm-18.4mm.
[0083] It should be noted that when analyzing the tensile strain capacity of girth welds with unequal wall thickness, if the distal strain at the moment of girth weld failure is taken as TSC, the distal strain on the thick-walled pipe side will be much smaller than the distal strain on the thin-walled side, but it cannot be interpreted as the strain capacity on the thick-walled side is smaller than the strain capacity on the thin-walled side. Considering the overall behavior of the pipeline structure, TSC is defined in this study as the average value of TSC on both sides of the girth weld.
[0084] The misalignment of the girth weld was also defined as a key parameter affecting strain capacity (TSC), and 0.8 mm was used as the general level and 1.6 mm as the higher level. To ensure conservative results, the defect size was defined as 25 mm × 4 mm, the location was the inner surface, and the crack tip was located on the fusion line.
[0085] Girth weld geometry
[0086] Seven typical weld macroscopic morphologies were selected at the pipeline site to identify the common features of the weld profiles. Figure 2 The weld macro-morphology of a typical wall thickness FCAW-S X80 steel grade pipe is shown in Figure 1. Based on the weld macro-morphology, three material regions can be identified: (1) pipe body base material, (2) HAZ, and (3) weld metal. The use of these three regions simplifies the modeling of material changes in the weld region while retaining key features. The dimensions of the boundaries between the material regions were measured and the seven weld macro-morphology images are listed in Table 1.
[0087] Table 1 Weld seam dimensions representing the boundaries between material zones
[0088]
[0089] A representative value is selected for each parameter based on the measurement results, as shown in the last row of Table 1. Then, based on the representative values of each wall thickness combination, a finite element analysis model of the girth weld is established, as shown in Figure 3 As shown. For girth welds with unequal wall thickness conditions, a 20° angle is added on the thicker side to characterize the inner groove. An internal surface crack defect with a height of 4 mm and a length of 25 mm is introduced, and the crack tip is located on the fusion line between the heat-affected zone and the weld metal on the thinner side of the girth weld to obtain a conservative TSC estimate.
[0090] Material properties in the finite element analysis model of girth welds
[0091] Three ultimate tensile strength levels of steel pipes were selected for material properties in the finite element analysis, as shown in Table 2. The lower and upper limits of the tensile strength of X80 steel are 634MPa and 772MPa, respectively. The 703MPa level represents the strength level of pipelines involved in multiple accidents. The yield strength (YS) of each level was then estimated based on the yield strength ratio. Generally speaking, higher tensile strength also corresponds to a higher yield strength ratio.
[0092] Table 2 Steel pipe strength in TSC analysis
[0093]
[0094]
[0095] Two softening levels of the heat affected zone are introduced in the finite element analysis of the fracture driving force, which are 10% and 20%. Due to the uneven strength of the heat affected zone material, the softening degree of the heat affected zone is defined as the relative difference between the minimum UTS of the heat affected zone and the UTS of the pipe outside the heat affected zone.
[0096] The apparent toughness CTODA of the weld metal is selected as 0.3mm, 0.45mm, 0.6mm, and 0.8mm. This is based on the fracture toughness test data of FCAW girth welds. This value can be understood as a common value, representing the girth weld using the usual FCAW welding process;
[0097] According to the parameter sampling of typical girth weld sections, such as Figure 3 As shown, the finite element geometry parameters and finite element model are constructed. The conditions analyzed are summarized in Table 3. The parameter types for selecting these conditions include the geometric characteristics of the pipeline and the girth weld, the material properties of the pipeline and the girth weld, and the calculation examples are 768;
[0098] Table 3 Fracture driving force analysis table Strain capacity calculation
[0099] The finite element analysis consists of two loading steps; in the first step, an internal pressure corresponding to a specific pressure coefficient is applied; in this step, both ends of the tube are fixed; in the second step, the internal pressure of the first step is maintained and a tensile displacement is applied to one end of the tube, while the other end is kept fixed. Figure 4 As shown, the crack tip opening displacement and distal strain are recorded to obtain the crack tip opening displacement (CTOD) and strain relationship. At a distance of one outer diameter from the girth weld, the strain value is obtained with a gauge length of one outer diameter, which is defined as the distal strain, which is used to represent the strain response of the pipe body under a specific load state.
[0100] According to the analysis conditions described in Table 3, the fracture driving force of the 1016mm outer diameter defective girth weld pipe under study was calculated, and the 0.3mm apparent toughness was determined in combination with the performance level of the actual FCAW process girth weld to obtain a conservative value of TSC. In addition, TSC was calculated for three apparent toughness levels of 0.3mm, 0.45mm, 0.6mm, and 0.75mm. In this way, the apparent toughness can also be used as a key input parameter for predictive evaluation in the developed TSC model.
[0101] When the apparent toughness is assumed to be δ = 0.3 mm, the TSC of each wall thickness combination is as follows: Figures 5 to 8 As shown. In each wall thickness combination, 12 cases were analyzed. The material parameters for all analysis conditions are listed in the table below the bar graph. For the case of unequal wall thickness connections, the average value of the remote strain on both sides of the weld is given as TSC. At the same time, for the introduction of misalignment under unequal wall thickness conditions, the thin-walled side is placed on the "high" side (or the "larger" outer diameter side) to ensure the conservatism of the analysis results.
[0102] The results of tensile strain capacity analysis under various conditions are as follows:
[0103] The tensile strain capacity under 12 cases is listed, and the TSC levels under five internal pressure conditions are given according to the weld mismatch ratio, high and low misalignment and the degree of softening in the heat-affected zone.
[0104] Conditions 1 to 4, 5 to 8, and 9 to 12 correspond to three weld metal strength matching levels. It can be seen that weld strength matching has an important influence on the TSC of the girth weld, and lower weld strength will significantly reduce the overall TSC.
[0105] The five data bars in each group represent the TSC under internal pressures of 0MPa, 5.6MPa, 7.0MPa, 8.4MPa and 10MPa, respectively. These internal pressure levels represent the conditions of design coefficients of 0, 0.4, 0.5, 0.6 and 0.72, which are also several typical working internal pressures of the pipeline. From the TSC analysis of the 12.8mm pipeline under different internal pressure conditions, it can be seen that for the condition of no internal pressure, the TSC of the high-strength matching girth weld is roughly twice the level when the design coefficient is 0.4, and after the design coefficient exceeds 0.4, the influence of internal pressure on TSC is small.
[0106] Conditions 1-2, 5-6, 9-10 represent the 0.8mm misalignment conditions under three matching degrees, and 3-4, 7-8, 11-12 represent the 1.6mm misalignment conditions. The analysis results show that under higher welding matching degrees, when TSC is higher, it can be seen that the misalignment has a significant effect on TSC. When the matching degree is lower, the effect of the misalignment is not obvious.
[0107] For each misalignment level, the two data bars represent the degree of HAZ softening at 10% and 20%, respectively. Similar to the misalignment, when the weld matching is high, the HAZ softening has a greater impact on TSC, while under low-strength matching conditions, the influence of HAZ softening is limited due to the small TSC value.
[0108] Under the condition of high matching girth weld, the influence of internal pressure and misalignment on TSC of girth weld is more significant. This can also be understood that for girth weld with low strength matching, the influence of internal pressure and misalignment on TSC is often masked by the influence of strength matching.
[0109] like Figure 5 and Figure 8 As shown in the figure, the TSC of the girth welds connecting pipes with different wall thicknesses deserves special attention. When the girth welds with different wall thicknesses are subjected to longitudinal tension, due to the same axial load, the axial stress on the thin-walled side is greater than the axial stress on the thick-walled side due to the difference in cross-sectional area. In this case, the strain on the thin-walled side is larger. The thicker side enters the plastic stage later, resulting in the TSC not being higher than 0.4% even if the average strain on both sides is used as an indicator. The influence of different parameters on the strain capacity of the thin-walled side is similar to the influence on the strain capacity of the girth weld of the same wall thickness pipe.
[0110] When conducting TSC evaluation of girth welds of unequal wall thickness pipelines, the strain demand and strain capacity of the same girth weld should be compared. Generally speaking, the strain demand of the environment on the pipeline is determined. Although generally speaking, the thick-walled side has a greater strain capacity than the thin-walled side, for unequal wall thickness connecting pipelines, the thick-walled and thin-walled sides use the same failure trigger event, resulting in the thin-walled side having a greater strain capacity numerically. From the perspective of the overall structure of the pipeline, the average strain on both sides of the girth weld can be considered as the tensile strain capacity of the pipeline.
[0111] Combined with the actual working conditions of the pipeline project, different levels of settings were made for the possible nine factors (variables), and on this basis, the fracture driving force was calculated, and the tensile strain capacity calculation results of the girth weld joint were obtained using the crack initiation criterion as the failure criterion. According to the results of the TSC evaluation within the effective range. The specific method of multivariate grid interpolation is as follows:
[0112] 1) In order to reduce the impact of unit and scale differences between different features, some parameters are normalized:
[0113] f p =P d D / 2t min σ y Pressure coefficient
[0114] ξ=σ y / σ b Base material yield strength ratio
[0115] α=(t max -t min ) / t min Normalized unequal wall thickness difference
[0116] η=Δ / t min Normalized misalignment
[0117] Among them, f p is the pressure coefficient, P d is the operating pressure, D is the pipe diameter, t min is the minimum wall thickness, t max is the maximum wall thickness, ξ is the yield strength ratio of the parent material, σ y is the yield strength of the parent material, σ b is the tensile strength of the base material, α is the normalized unequal wall thickness difference, η is the normalized misalignment, and Δ is the misalignment.
[0118] 2) For the specific working condition parameters of the pipeline in this study, the results can be linearly interpolated according to the wall thickness (combination), apparent toughness, misalignment, HAZ softening degree, weld metal matching, and internal pressure parameters, and the multivariate linear interpolation function of TSC calculation can be constructed by combining the normalized parameter grid space:
[0119] TSC=F(f p ,ξ,α,η,δ A ,λ)
[0120] Among them, δA represents the fracture toughness level, and λ represents the degree of softening in the heat-affected zone. This function can be used to realize TSC calculation under specific operating parameters, and introduces parameters such as unequal wall thickness connection, misalignment, heat-affected zone softening, weld metal strength matching, operating pressure, and apparent toughness. Each parameter can be input within its specific effective range. The apparent toughness level can be obtained through the conversion relationship between impact toughness or fracture toughness. By inputting the above key parameters, the tensile strain capacity of in-service pipelines can be effectively evaluated from an engineering perspective, providing a convenient and practical tool for evaluating the ability of in-service pipelines to resist strain caused by geological disasters.
[0121] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.
[0122] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any ordinary technician in the industry can smoothly implement the present invention as shown in the drawings and described above. However, any equivalent changes, modifications and evolutions made by technicians familiar with the profession without departing from the scope of the technical solution of the present invention using the technical content disclosed above are all equivalent embodiments of the present invention. At the same time, any equivalent changes, modifications and evolutions made to the above embodiments based on the essential technology of the present invention are still within the protection scope of the technical solution of the present invention.
Claims
1. A method for predicting the tensile deformation capacity of an in-service pipeline, characterized in that: include, Through pipeline tensile test, the tensile stress-strain relationship of different regions of pipeline and girth weld is obtained, so as to obtain the tensile properties of different regions of pipeline; Establishing a finite element analysis model of a girth weld containing defects according to relevant parameters of the pipeline and the girth weld joint; the finite element analysis model of the girth weld containing defects includes a maximum allowable defect; By introducing the tensile properties of different regions of the pipeline into the finite element analysis model of the girth weld with defects, and then analyzing the finite element analysis model of the girth weld with defects, tensile deformation is applied to the pipeline in the analysis to obtain the fracture driving force information during the crack propagation process; Based on the fracture driving force information and combined with the different levels of fracture toughness indexes of pipeline girth welds, a database of tensile strain capacity under different conditions of pipeline geometric characteristics and material properties is obtained; According to the tensile strain capacity database, the tensile strain capacity of pipelines under different parameter conditions is predicted and evaluated by multivariate grid interpolation method.
2. A method for predicting the tensile deformation capacity of an in-service pipeline according to claim 1, characterized in that: The specific process of obtaining the tensile properties of the pipeline is: A longitudinal sample is taken from the pipeline, and the engineering stress-strain curve of the pipeline is obtained through a tensile test, and the tensile stress-strain relationship of the pipeline is obtained, thereby obtaining the tensile properties of the pipeline; the specifications of the longitudinal sample are a gauge width of 38.1 mm and a gauge length of 50.8 mm.
3. The method for predicting the tensile deformation capacity of an in-service pipeline according to claim 1, characterized in that: The specific process of establishing the finite element analysis model of the girth weld with defects is as follows: Select multiple representative values for each parameter of the relevant parameters of the pipeline and the girth weld joint, combine the representative values of each wall thickness combination between girth weld joints with different wall thicknesses, and jointly establish a finite element analysis model of the girth weld with defects; The relevant parameters of the pipeline and girth weld joint include performance parameters, geometric characteristics and defect parameters of the pipeline and girth weld; The performance parameters of the pipeline and girth weld joint include the apparent toughness of the pipeline and girth weld, the strength and matching relationship of the pipe body and weld metal, and the softening degree of the heat-affected zone; The geometrical features of the pipeline and the girth weld include the outer diameter of the pipeline, the wall thickness of the pipeline, the misalignment amount of the girth weld and the defect size. The wall thickness of the pipeline includes the unequal wall thickness of the girth weld joint.
4. A method for predicting the tensile deformation capacity of an in-service pipeline according to claim 3, characterized in that: The defect dimensions include cap width, cap weld height, root weld height, root weld width, HAZ width and groove angle.
5. The method for predicting the tensile deformation capacity of an in-service pipeline according to claim 1, characterized in that: The specific process of obtaining the fracture driving force information during crack propagation is as follows: According to the defects, load level and material properties of the pipeline, a tensile deformation analysis was performed on the finite element model of the defective girth weld. In the analysis, axial tensile deformation was applied to the pipeline to obtain the crack tip opening displacement data of the pipeline weld defect and its relationship with the tensile strain of the pipeline, thereby obtaining the characterization of the girth weld fracture driving force. By setting the ordinate to the fracture driving force expressed by the crack tip opening displacement and the abscissa to the tensile strain of the pipeline, the pipeline weld fracture driving force curve information during the crack propagation process was obtained.
6. A method for predicting the tensile deformation capacity of an in-service pipeline according to claim 5, characterized in that: The load level includes the internal pressure to which the pipeline is subjected, and the material properties include the yield strength, tensile strength, and heat-affected zone softening of the pipeline.
7. The method for predicting the tensile deformation capacity of an in-service pipeline according to claim 1, characterized in that: The fracture toughness index value of the material is obtained by characterizing the apparent toughness of the weld metal under different conditions.
8. A method for predicting the tensile deformation capacity of an in-service pipeline according to claim 7, characterized in that: The pipeline weld fracture driving force data and the material fracture toughness index value are combined, and the pipeline tensile strain capacity data are obtained through the intersection value between the fracture driving force curve of the pipeline weld under different parameter conditions and the apparent toughness.
9. The method for predicting the tensile deformation capacity of an in-service pipeline according to claim 1, characterized in that: According to the multivariate grid interpolation method, the specific process of evaluating and predicting the tensile strain capacity of pipelines under different parameter conditions is as follows: The results of the tensile strain capacity of the pipeline are interpolated by linear grids through the specific working condition parameters of the pipeline, and then the relevant parameters of the pipeline and the girth weld joint are normalized. The relevant parameters of the normalized pipeline and the girth weld joint are combined with the linear grid interpolation to construct a multivariate linear interpolation function for strain capacity calculation in the grid space. The specific formula is: TSC=F(f p ,ξ,α,η,δ A ,l) Among them, δA represents the fracture toughness level, λ represents the softening degree of the heat affected zone, and f p is the pressure coefficient of the pipeline, ξ is the yield strength ratio of the pipeline base material, α is the normalized unequal wall thickness difference, η is the normalized misalignment; TSC is the strain capacity; The specific working condition parameters of the pipeline include pipeline wall thickness, apparent toughness, girth weld misalignment, heat affected zone softening degree, weld metal matching degree and internal pressure parameters.
10. A method for predicting the tensile deformation capacity of an in-service pipeline according to claim 9, characterized in that: The relevant parameters of the normalized pipeline and girth weld joint include: The pressure coefficient of the pipe is f p =P d D / 2t min σ y ; The yield strength ratio of the pipe base material is ξ=σ y / σ b ; The difference in wall thickness of the girth weld joint is α=(t max -t min ) / t min ; The misalignment of the girth weld is η = Δ / t min ; Among them, f p is the pressure coefficient of the pipeline, P d is the operating pressure of the pipeline, D is the diameter of the pipeline, t min is the minimum wall thickness of the girth weld, t max is the maximum wall thickness of the girth weld joint, ξ is the yield strength ratio of the pipe base material, σ y is the yield strength of the pipe base material, σ b is the tensile strength of the pipe base material, α is the normalized unequal wall thickness difference, η is the normalized misalignment, and Δ is the misalignment.