CN115374677A - Method for evaluating safety of pipeline with crack defects under landslide geological disaster - Google Patents
Method for evaluating safety of pipeline with crack defects under landslide geological disaster Download PDFInfo
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Abstract
The invention discloses a method for evaluating the safety of a pipeline with crack defects under landslide geological disasters, belongs to the field of pipeline geological disaster safety evaluation, and aims to provide a method for evaluating the safety state of a pipeline with crack defects under the action of landslide geological disasters, obtaining a pipeline critical fracture toughness value by analyzing the pipeline fracture toughness adaptability, establishing a landslide lower displacement stress calculation model to obtain landslide lower stress displacement, judging the pipeline safety state based on two criteria of yield strength and fracture toughness, and quantitatively analyzing the pipeline safety state.
Description
Technical Field
The invention relates to the field of oil and gas pipeline safety conveying, in particular to pipeline safety evaluation under the double risk coupling effect of a pipeline passing through a landslide geological disaster point in a mountainous area and a pipeline body containing crack defects.
Background
The oil and gas pipeline is used as a main mode for energy transmission, the quantity is large, the distribution is wide, complex regional environments of mountains, rivers and ravines are needed to pass along the line, and regional intersection is large. The complex wiring environment poses a serious challenge to the safe operation of the pipeline, landslide is one of the geological hazards, the pipeline safety protection device has the characteristics of strong burst property and large destructive power, and can seriously affect the safety of the pipeline. Under the action of landslide, the pipeline is easy to break, collapse, move greatly, expose the pipe and the like, and according to statistics, the west-east gas transmission pipeline is up to 155 parts along the landslide, and the puckery-blue gas transmission pipeline is distributed at 13 parts along the landslide, and is damaged correspondingly to high consequences. The pipeline has certain level of strength and rigidity, meets requirements for resisting common small and medium landslides, and fails when the critical bearing capacity of the pipeline is exceeded when large-scale landslides are met, so that the evaluation of the safety of the pipeline under the landslide effect has important significance for ensuring the long-term operation of the pipeline. The long-distance oil and gas pipeline is formed by welding 10 m-12 m pipe joints, although the pipeline is physically connected, the pipeline is easy to have some defects caused by the discontinuity of materials, such as incomplete welding of the connection part and existence of cracks. The presence of cracks not only leads to further discontinuities in the material but also to discontinuities in the mechanical state, and stress concentrations tend to occur in the vicinity of the cracks. The presence of cracks on the pipe is an exponential compromise on pipe strength, some pipes, while not reaching the yield limit, quickly develop a fracture failure due to the presence of cracks. Traditional landslide safety evaluations are based on pipeline integrity conditions, the evaluation method for the pipeline containing the crack defects does not meet the use requirements. Based on the problems, the invention provides a method for evaluating the safety of a pipeline with crack defects under the action of a landslide.
Disclosure of Invention
The invention aims to provide a method for evaluating the safety of an oil-gas pipeline with defects under the action of a landslide, which judges the safety state of the pipeline by analyzing the relationship between the axial stress and the fracture toughness of the pipeline and the parameters of yield strength and critical fracture toughness, and finally achieves the aim of quantitatively evaluating the risk of the pipeline.
Drawings
In order to show the embodiments and technical solutions of the present invention more clearly, the embodiments or the prior art will be briefly described below with reference to the accompanying drawings, which are only some embodiments of the present invention.
FIG. 1 is a flow chart of the safety evaluation of a pipeline with crack defects under the action of landslide.
Detailed Description
Aiming at the problems, the invention aims to provide a method for evaluating the safety of a pipeline with crack defects under the action of a landslide, which is used for correctly evaluating the safety risk level of the pipeline by analyzing the relation between force applied by the landslide and stress applied to the pipeline.
The technical scheme of the invention is as follows:
a method for evaluating the safety of a pipeline containing crack defects under landslide geological disasters comprises the following steps:
s1: collecting design parameters of the pipeline and operation condition data, wherein the design parameters comprise pipe diameter, wall thickness, burial depth, steel grade, steel yield strength and tensile strength, and the operation condition data are pipeline internal pressure;
s2: collecting landslide quantitative characterization parameters, wherein the landslide quantitative characterization parameters specifically comprise landslide soil density, and height and width of a landslide possibly generated;
s3: collecting detection data of the pipeline in the calendar year, specifically comprising weld inspection data and internal thickness measurement data, interpreting the position of a crack defect of the pipeline and the size of the crack according to the internal detection data, normalizing the size of the crack, and giving a length value and a width value for describing the size of the crack;
s4: carrying out pipeline fracture toughness adaptability analysis, carrying out a three-point bending experiment by adopting a sample made of the same material as the pipeline, screening out fracture toughness parameters suitable for the pipeline material, and simultaneously obtaining critical fracture toughness parameters based on the three-point bending experiment, wherein the fracture toughness parameters mainly comprise a stress intensity factor K, crack tip opening displacement CTOD and J integral;
s5: establishing a landslide-pipeline mechanical coupling calculation model, taking a pipeline as a cross beam based on a soil spring model, establishing a pipeline mechanical model under the landslide effect, and calculating the stress displacement distribution of the pipeline without defects;
s6: establishing a finite element calculation model of the pipeline with the crack defects, taking the stress displacement distribution obtained in the step S5 as a finite element calculation boundary condition, and obtaining a fracture toughness parameter through finite element calculation;
s7: and evaluating the safety state of the pipeline, judging whether the pipeline is safe or not based on the yield strength and fracture toughness parameters, and quantitatively giving the grade of the safety state of the pipeline.
Preferably, in step S4, the three-point bending test is performed to analyze the adaptability of the pipeline fracture toughness parameter and measure the pipeline critical fracture toughness parameter, and the determination is performed by the following steps:
s41: sampling on a pipeline, sampling along the axial direction of the pipeline, uniformly taking 8 samples, wherein the 8 samples are cuboid samples, the length of each sample is 80mm, the width of each sample is 20mm, the thickness of each sample is 10mm, the samples are distributed annularly along the pipeline, and the spacing distance between every two samples is 45 degrees;
s42 the method comprises the following steps: performing mechanical crack cutting on the sample S41 by adopting a molybdenum wire with the thickness of 0.12mm, wherein the crack position is in the middle of the sample, the penetration thickness direction is realized, and the crack length is 10mm;
s43: performing fatigue crack prefabrication on the S42 mechanical crack notch, placing a sample into a three-point bending pressure rod, starting three-point bending, setting the maximum displacement of a three-point bending testing machine to be 0.8mm, and performing up-and-down reciprocating circulation, wherein the number of experimental circulation times is 100;
s44: putting the sample subjected to fatigue crack prefabrication in the S43 three-point bending testing machine again, installing an extensometer with the gauge length not exceeding 10mm at the position of a crack mouth, starting an experiment, slowly descending a three-point bent rod, and measuring a load vertical displacement curve and a load crack mouth opening displacement curve through the extensometer and a three-point bent rod self-contained displacement system in the descending process;
s45: in the experiment process, when the sound of bang is heard, the experiment is stopped, and the sample is taken down;
s46: analyzing the load vertical displacement curve and the load crack mouth opening displacement curve obtained in the S44 and the S45, wherein the curve initially rises with a certain slope, the slope of the curve gradually decreases after the curve rises to a certain degree, and finally the curve has an inflection point and descends;
s47: analyzing the opening displacement curves of the load crack mouths obtained in the S44 and the S45, making a curve with the slope 5% smaller than that of the initial curve along the starting point, intersecting the curve and the opening displacement curve of the crack mouths at a point, and setting the horizontal and vertical coordinates corresponding to the point as the critical loads Pc and Vc for crack initiation;
s48: analyzing the load vertical displacement curves obtained in S44 and S45, finding a point corresponding to the critical load Pc obtained in S47 on the curve, taking the point as a starting point, making an oblique line parallel to the initial curve, intersecting the oblique line with the abscissa at a point, and obtaining the area enclosed by the oblique line, the load vertical displacement curve and the abscissa, namely the plastic deformation work Up under critical crack initiation;
s49 the method comprises the following steps: solving a critical stress intensity factor Kc according to the critical load Pc obtained in S47, wherein the critical stress intensity factor Kc is solved by the following formula:
in the formula: p is pressure, N; s is span, mm; b is the thickness of the sample, mm; w is the width of the sample, mm; a is the length of the crack, mm; k is stress intensity factor, MPa.mm 0.5 ；
S410: and solving the critical CTOD according to the critical load Vc obtained in the step S47 and the critical Kc obtained in the step S49, wherein the critical CTOD is solved through the following formula:
δ＝δ e +δ p
in the formula: delta. For the preparation of a coating e Elastic displacement, mm; delta p Plastic displacement, mm; r is a twiddle factor, and takes 0.4 in the standard; w is the width of the test piece, mm; v p To be tested the maximum opening displacement is realized by the following steps, mm; a is the crack length, mm; e is the elastic modulus, MPa; sigma s Yield strength, MPa;
s411 to Annuncis Koreana the method comprises the following steps: solving a critical J integral according to the critical load Up obtained in S48 and the critical Kc obtained in S49, wherein the critical J integral is solved according to the following formula:
in the formula: j. the design is a square p Is the J integral plastic fraction; j. the design is a square e Integrating the elastic part for J;
s412: judging the critical fracture toughness, and determining delta in S410 e And δ, J in S411 e Comparing with J, if delta e Delta is different from delta by less than 10%, and J e If the difference between the value of the integral and the value of J is less than 10%, selecting the critical stress intensity factor Kc obtained by S49 for fracture toughness, and if the value of the integral does not meet the formula, selecting the critical J integral obtained by S411 for fracture toughness;
s413: and determining a critical fracture toughness parameter after judging the critical fracture toughness according to the S412, and determining an absolute value of the critical fracture toughness parameter to serve as a subsequent safety evaluation method.
Preferably, in step S5, a landslide-pipeline mechanical coupling calculation model is established, and the calculation steps are as follows:
s51: the external force calculation formula of landslide soil acting on a unit length pipeline is as follows:
F 1 ＝ρ sliding body gh 1 Dsinθ 1
In the formula: f 1 Is landslide soil the physical strength of the human body, N; rho Sliding body Is the density of landslide soil, kg/m 3 (ii) a g is gravitational acceleration of 9.8m/s 2 ；h 1 Is the height of the landslide mass, m; d is the outer diameter of the pipeline, m; theta 1 Is a landslide body the inclination angle of the inclined plate is changed, (iv) DEG;
s52: the reaction force calculation formula of the foundation reaction force acting on the pipeline is as follows:
F 2 ＝k 1 yD
in the formula: f 2 The counter force is the action of sinking the pipeline to the foundation, N; k is a radical of 1 Is the ground coefficient, N/m 3 (ii) a y is different positions of the pipeline the sinking displacement of the moving body (c), or becomes deflection, m; d is the outer diameter of the pipeline, m;
s53: the formula for calculating the counter force generated by the friction force in the landslide process is as follows:
F 3 ＝ρ soil for soil gh 2 Dk 2 cosθ 2
In the formula: f 3 Force generated by friction, N; rho Soil for soil The density of the soil above the pipeline during backfilling is kg/m 3 ；h 2 M is the buried depth of the pipeline; k is a radical of 2 The friction coefficient is generally 0.3; theta 2 Is the inclination angle of the pipeline axis deviating from the horizontal degree;
s54: and (5) solving the bending moment of the pipeline along the line by integrating S51, S52 and S53 to obtain a pipeline bending moment calculation formula as follows:
in the formula: l is 1 Is the landslide area length, m; l is 2 Is the length of the landslide impact area, m;
s55: according to an S54 pipeline bending moment equation along the pipeline and in combination with a pipeline bending equation, a pipeline deflection calculation formula under the landslide action is obtained as follows:
s56: solving the S55 pipeline deflection curve by adopting a finite difference method to obtain the deflection y along the pipeline;
s57: substituting the pipeline deflection obtained in the step S56 into a pipeline bending moment calculation equation in the step S54 to obtain a bending moment, and solving the axial stress of the pipeline under the landslide action by adopting the following formula;
in the formula: i is z Is the pipe section moment of inertia, m 4 And y is the position from the pipeline section to the neutral axis, m.
Preferably, in step S6, a finite element calculation model of the pipeline including the crack defect is established, and the pipe deflection obtained in step S56 is used for both ends of the pipeline in the finite element model while using the fixed boundary conditions.
Preferably, in step S6, the finite element model takes into account the internal pressure, and the internal pressure value is the internal pressure collected in step S1.
Preferably, in the finite element model in step S6, the position of the crack is pre-determined at the middle position of the landslide, and the size of the crack is determined according to step S3.
Preferably, the finite element model in step S6 requires an output fracture toughness parameter, which is determined according to step S412.
As a matter of preference, the safety state of the pipeline is evaluated in step S7, the method comprises the following steps:
s71: comparing the axial stress of the pipeline obtained in the step S57 and the fracture toughness of the pipeline obtained in the step S6 with the yield strength of the pipeline and the critical fracture toughness obtained in the step S413;
s72: if one of the axial stress and the fracture toughness value of the pipeline is greater than the yield strength or the critical fracture toughness of the pipeline, the pipeline is a dangerous pipeline and needs to be stopped to be repaired;
s73: if the values of the axial stress and the fracture toughness of the pipeline are both smaller than the yield strength or the critical fracture toughness of the pipeline, the pipeline safety risk level needs to be given.
Preferably, the step S73 of evaluating the pipeline safety risk level comprises the following steps:
when the axial stress of the pipeline is 20% -50% of the yield strength, the critical fracture toughness is below 50% and is low risk, 50% -80% is medium risk, and 80% -100% is high risk section;
when the axial stress of the pipeline is 50% -80% of the yield strength, the critical fracture toughness is lower than 30% and is low risk, 30% -60% is medium risk, and 60% -100% is a high risk section;
when the axial stress of the pipeline is 80% -100% of the yield strength, the critical fracture toughness is below 10% and is low risk, 10% -40% is medium risk, and 40% -100% is high risk section.
Claims (3)
1. A method for evaluating the safety of a pipeline with crack defects under landslide geological disasters is characterized by comprising the following steps:
step 1, collecting pipeline design parameters and operation condition data, wherein the design parameters comprise pipe diameter, wall thickness, burial depth, steel grade, steel yield strength and tensile strength, and the operation condition data are pipeline internal pressure;
step 2, collecting landslide quantitative characterization parameters, specifically comprising landslide soil mass density and landslide possible height and width;
step 3, collecting detection data of the pipeline in the calendar year, specifically comprising weld inspection data and internal thickness measurement data, judging the position of a crack defect of the pipeline and the size of the crack according to the internal detection data, normalizing the size of the crack, and giving a length value and a width value for describing the size of the crack;
step 4, carrying out pipeline fracture toughness adaptability analysis, carrying out a three-point bending experiment by adopting a sample made of the same material as the pipeline, screening out fracture toughness parameters suitable for the pipeline material, and simultaneously obtaining critical fracture toughness parameters based on the three-point bending experiment, wherein the fracture toughness parameters mainly comprise a stress intensity factor K, crack tip opening displacement CTOD and J integral;
step 5, establishing a landslide-pipeline mechanical coupling calculation model, taking the pipeline as a cross beam based on the soil spring model, establishing a pipeline mechanical model under the landslide effect, and calculating the stress displacement distribution of the pipeline without defects;
step 6, establishing a finite element calculation model of the pipeline with the crack defects, taking the stress displacement distribution obtained in the step 5 as a finite element calculation boundary condition based on the stress displacement distribution, and obtaining fracture toughness parameters through finite element calculation;
and 7, evaluating the safety state of the pipeline, judging whether the pipeline is safe or not based on the yield strength and fracture toughness parameters, and quantitatively giving the grade of the safety state of the pipeline.
2. The method for evaluating the safety of the pipeline with the crack defects under the landslide geological disaster according to claim 1, wherein in the step 5, a landslide-pipeline mechanical coupling calculation model mainly comprises the following steps:
step a, calculating the external force of landslide soil acting on a unit length pipeline according to the following formula:
F 1 ＝ρ sliding body gh 1 Dsinθ 1
In the formula: f 1 Landslide soil physical strength, N; zxfoom ρ Sliding body Is the density of landslide soil in kg/m 3 Zxfoom g is gravitational acceleration of 9.8m/s 2 ；h 1 M is the height of the landslide body; d is the outer diameter of the pipeline, m; theta 1 Is the slope angle of the landslide body;
step b, a reaction force calculation formula of the foundation reaction force acting on the pipeline is as follows:
F 2 ＝k 1 yD
in the formula: f 2 A counterforce acting on the pipeline sinking foundation, N; k is a radical of 1 Is the ground coefficient, N/m 3 Zxfoom y is the sinking displacement of different positions of the pipeline or becomes deflection m; d is the outer diameter of the pipeline, m;
step c, a counter force calculation formula generated by friction force in the landslide process is as follows:
F 3 ＝ρ soil for planting gh 2 Dk 2 cosθ 2
In the formula: f 3 Force generated by friction, N; rho Soil for planting The density of the soil above the pipeline during backfilling is kg/m 3 ；h 2 M is the buried depth of the pipeline; k is a radical of 2 The friction coefficient is generally 0.3; theta 2 Is the inclination angle of the pipeline axis deviating from the horizontal degree;
step d, solving the bending moment of the pipeline along the line position in the steps a, b and c to obtain a pipeline bending moment calculation formula as follows:
in the formula: l is 1 Is the landslide area length, m; l is 2 The length of the landslide influence area is m;
step e, according to the bending moment equation along the pipeline in the step d and in combination with the pipeline bending equation, obtaining a pipeline deflection calculation formula under the landslide action as follows:
step f, solving the deflection curve of the pipeline in the step e by adopting a finite difference method to obtain the deflection y along the pipeline;
step g, the following steps: substituting the pipe deflection obtained in the step f into a pipe bending moment calculation equation obtained in the step d to obtain a bending moment, and solving the axial stress of the pipe under the landslide action by adopting the following formula;
in the formula: i is z Is the pipe section moment of inertia, m 4 And y is the position from the pipeline section to the neutral axis, m.
3. The method for evaluating the safety of the pipeline with the crack defects under the landslide geological disaster according to claim 1, wherein in the step 7, the step of determining the safety state grade of the pipeline comprises the following steps:
step a, when the axial stress of the pipeline is 20% -50% of the yield strength, the critical fracture toughness is below 50%, the risk is low, 50% -80% is medium, and 80% -100% is a high-risk section;
step b, when the axial stress of the pipeline is 50% -80% of the yield strength, the critical fracture toughness is below 30% and is low risk, 30% -60% is medium risk, and 60% -100% is a high risk section;
and c, when the axial stress of the pipeline is 80% -100% of the yield strength, the critical fracture toughness is lower than 10%, 10% -40% is middle risk, and 40% -100% is a high risk section.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN117077496A (en) * | 2023-10-16 | 2023-11-17 | 西南石油大学 | Safety evaluation method for pipeline containing corrosion defects under landslide effect |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN117077496A (en) * | 2023-10-16 | 2023-11-17 | 西南石油大学 | Safety evaluation method for pipeline containing corrosion defects under landslide effect |
| CN117077496B (en) * | 2023-10-16 | 2024-01-23 | 西南石油大学 | Safety evaluation method for pipeline containing corrosion defects under landslide effect |
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