Method for life testing of pipes with defects under laboratory conditions using uniaxial loading method of specimens

Abstract

FIELD: testing.SUBSTANCE: invention relates to testing the strength properties of full-scale specimens of pipes for transporting oil or petroleum products by applying mechanical forces to them, in particular to conducting life tests of pipes with defects. The method comprises the following steps: cutting out a full-scale pipe specimen from the mains pipe section; measuring the geometric characteristics of the full-scale pipe specimen with a defect and the geometric parameters of the longitudinal weld; determining the strength properties of the pipe metal by tensile testing the metal specimens; creating a digital model of the full-scale pipe specimen with a defect and a model of a laboratory pipe specimen with a defect, calculating the expected number of cycles until the complete failure of the digital model of the specimen using the finite element method; manufacturing laboratory specimens and conducting tests using the cyclic uniaxial loading method, determining the residual life of the mains pipe process section with a defect.EFFECT: increase in the reliability of determining the residual life of pipelines with defects.7 cl, 9 dwg, 1 tbl

Description

[0001] The invention relates to the field of studying the strength properties of full-scale samples of pipes for transporting oil or petroleum products by applying mechanical forces to them, in particular to conducting resource tests of pipes with defects using laboratory equipment for assessing the residual life of pipelines with defects.

[0002] The closest analogue to the invention is the invention "Method for testing pipes for durability", disclosed in patent RU 2591873 C1 (published on 20.07.2016, IPC G01N 3 / 32). The method for testing pipes for durability, which consists in the fact that a full-scale pipe sample is mounted on a test bench with plugs welded to the ends of the pipe being tested, wherein one of the plugs is equipped with drainage and drain nozzles, testing the full-scale pipe sample for durability by loading with cyclic internal pressure in the range from the minimum pressure P min up to maximum pressure P max , and P maxcorresponds to the highest excess pressure during pipeline operation in the standard mode P норм , and the value of P min does not exceed 0.1 P max , and cyclic bending of a full-scale pipe sample by applying a bending moment to it with a change in the excess bending radius ρ изг full-scale sample in the range of 40 D н <ρ изг <1000 D н , where D н - the outer diameter of the pipe being tested; in this case, loading with internal pressure is performed at a given frequency ω p , and the frequency ω изг loading of a full-scale specimen by cyclic bending is in the range of 0.003 ω p <ω изг <ω pDurability tests on a full-scale pipe specimen are conducted until the specimen fails or becomes depressurized; based on the results of testing a full-scale pipe specimen, the parameters determining its durability are recorded: the number of loading cycles N, the value of the maximum and minimum pressure and / or bending moment before the specimen fails or becomes depressurized.

[0003] A disadvantage of this method is that expensive rig tests using a biaxial loading scheme are required to experimentally confirm the durability of defects and their combinations in the tested pipe. This method requires a full-scale pipe specimen and welded plugs to its ends for subsequent hydraulic testing, which can take a long time (4 to 7 days). The potential volume of full-scale pipe specimens tested is limited by the rig's capacity, and the tests themselves require a significant amount of time to accumulate the necessary statistics. Furthermore, testing using a biaxial loading system significantly increases the cost of testing and the labor required to manufacture and prepare the specimens. Furthermore, such testing requires expensive and highly specialized equipment.

[0004] The technical problem that the claimed invention is aimed at solving is to reduce the time and material costs of conducting resource tests of pipes in laboratory conditions using a uniaxial loading scheme for the tested full-scale samples.

[0005] The technical result achieved by implementing the claimed invention consists in increasing the reliability of determining the residual life of pipelines with defects based on a theoretical calculation confirmed by cyclic tests under laboratory conditions with a uniaxial loading scheme for laboratory samples.

[0006] The specified technical problem is solved, and the technical result is achieved, due to the fact that the method for conducting resource tests of pipes with defects in laboratory conditions by the method of uniaxial loading of samples requires the sequential implementation of the following stages:

[0007] - select a process section of the main pipeline (MP) with a defect;

[0008] - cutting out a full-scale sample of a pipe from the MT process section;

[0009] - measure the geometric characteristics of a full-scale pipe sample with a defect and the geometric parameters of the longitudinal weld seam;

[0010] - at least two samples of pipe metal are cut from a full-scale pipe sample for tensile testing;

[0011] - determine the strength properties of the pipe metal by testing metal samples for tension;

[0012] - create a digital model of a full-scale sample of a pipe with a defect based on the geometric characteristics of the full-scale sample of the pipe with a defect and the geometric parameters of the longitudinal weld;

[0013] - calculate equivalent stresses σ экв at the top of the defect of the digital model of a natural pipe sample using the finite element method;

[0014] - create a digital model of a laboratory pipe sample with a defect based on the geometric characteristics of the laboratory pipe sample with a defect and the geometric parameters of the longitudinal weld, the strength characteristics of the pipe metal samples using equivalent stresses σ экв at the top of the defect of the digital model of the natural pipe sample, calculated at the previous stage;

[0015] - the selection of uniaxial tensile forces from the grips of the testing machine on the digital model of the laboratory sample is carried out, which create stresses at the top of the defect equivalent to the stresses at the top of the defect of the digital model of the full-scale pipe sample with the defect, while the selection of forces from the grips is carried out iteratively, with control of the equivalent stresses σ экв in the defect area, and the selection of forces is considered complete when the maximum equivalent stresses σ эквat the top of the defect in the digital model of the laboratory sample become equal to the maximum equivalent stresses at the top of the defect in the digital model of the full-scale sample, under the action of loads corresponding to the internal pressure p and the bending moment M max technological section of MT;

[0016] - calculate the expected number of cycles until the complete destruction of the digital model of the sample using the finite element method;

[0017] - at least two laboratory samples are manufactured according to the geometric characteristics of the laboratory sample of a pipe with a defect, by cutting it from a full-scale sample of a pipe with the application of an artificial defect identical to the defect of the full-scale sample of the pipe, wherein each laboratory sample is a flat full-thickness element of a pipe corresponding to the thickness of the pipe wall metal δ with identical geometric parameters of the longitudinal weld seam of the pipe;

[0018] - at least two laboratory specimens are tested using the cyclic uniaxial loading method with an asymmetry coefficient of 0.1 until their failure with a maximum axial tensile force in a cycle, the value of which was determined during the selection of forces on a digital model of a specimen with a defect, while the tests using the uniaxial loading method are carried out ensuring that the temperature of the laboratory specimens is not higher than plus 40°C;

[0019] - determine the residual life of the technological section of the MT with a defect by comparing the results of calculations and the results of laboratory tests to determine the number of cycles until the complete destruction of the digital model of the laboratory sample and laboratory samples.

[0020] The development and refinement of the proposed invention are the following features, according to which:

[0021] - the geometric characteristics of a full-scale sample of a pipe with a defect are the outer diameter of the pipe D н, pipe wall thickness δ, defect length L, defect width W, defect depth h, defect location on a natural pipe sample;

[0022] - the geometric characteristics of a laboratory pipe sample with a defect are: the working length of the sample; the width of the sample b; the width of the head of the sample H; the radius of the mating part of the working part with the head of the sample R, the width of the defect W, the depth of the defect h;

[0023] - the geometric parameters of the longitudinal weld seam are the height of the outer seam reinforcement, the height of the inner seam reinforcement, the offset of the axes of the outer and inner seams, the width of the outer seam reinforcement, the width of the inner seam reinforcement, the offset of the edges, and the overlap of the seams;

[0024] - the strength characteristics of pipe metal samples are the yield strength σ т , ultimate strength σ в and relative elongation at break σ s ;

[0025] - a digital model of a full-scale pipe sample with a defect and a digital model of a laboratory sample are created in the ANSYS software package using the finite element modeling method;

[0026] - the expected number of cycles before the failure of the digital model of the laboratory sample is performed in the ANSYS Fatigue software package, taking into account the predicted change in the size of the defect with the rebuilding of the finite element mesh.

[0027] The claimed invention is illustrated by the following drawings: Fig. 1 schematically shows the parameters of the digital model of a full-scale pipe sample with a defect; Fig. 2 schematically shows the parameters of the digital model of the defect; Fig. 3 shows a digital model of a full-scale pipe sample with a defect with an applied finite element mesh; Fig. 4 shows the distribution of equivalent stresses over a section of the digital model of a full-scale pipe sample with a defect; Fig. 5 shows a digital model of a laboratory pipe sample with a defect with an applied finite element mesh; Fig. 6 shows the application of boundary conditions to the digital model of a laboratory pipe sample with a defect; Fig. 7 shows the zone of plastic deformation in the defect zone; Fig. 8 shows the predicted number of crack growth cycles along the boundary of the plastic deformation zone in the defect area after the first stage; Fig. 9 shows a general view of the laboratory sample with an applied defect in the center of the weld.

[0028] The following positions are indicated in Fig. 1-9:

[0029] 1 - defect;

[0030] 2 - weld seam with a defect applied in the center;

[0031] 3 - plastic deformation zone;

[0032] 4 - boundary of plastic deformation zone;

[0033] D н - outer diameter of the pipe;

[0034] R - radius of the mating of the working part with the sample head;

[0035] F - axial tensile force;

[0036] L - defect length;

[0037] H - width of the sample head;

[0038] W - defect width;

[0039] l - working length of the sample;

[0040] b - sample width;

[0041] δ - pipe wall thickness;

[0042] h - defect depth.

[0043] The declared method for conducting resource tests of pipes with defects in laboratory conditions using the uniaxial loading method of samples is carried out as follows.

[0044] Select a process section of the main pipeline (MP) with a defect (item 1) for which a determination of the remaining service life is required. A full-scale pipe sample is cut and the pipe's outside diameter D is then measured. н , the thickness of the pipe wall 3, the geometric parameters of the longitudinal weld (height of the outer weld reinforcement, height of the inner weld reinforcement, offset of the axes of the outer and inner welds, width of the outer weld reinforcement, width of the inner weld reinforcement, offset of the edges, overlap of the welds), as well as the length of the defect L, the width of the defect W, the depth of the defect h and fix the location of the defect (pos. 1) on the full-scale pipe sample.

[0045] From a full-scale pipe sample, metal samples are cut out for tensile testing in order to determine the strength properties of the pipe metal in the MT process section, such as the yield strength σ т , ultimate strength σ т, relative elongation at break δ5.

[0046] Create a digital model of a full-scale pipe specimen with a defect (item 1) using the ANSYS finite element modeling software. The finite element method is a numerical solution based on breaking down a complex geometric domain into multiple simpler subdomains called finite elements. This approach reduces complex partial differential equations to a system of algebraic equations, significantly simplifying the solution of solid mechanics problems with complex geometries and boundary conditions.

[0047] Based on the results of developing a digital model of a full-scale sample of a pipe with a defect, the equivalent stresses σ are calculated экв at the top of the defect of the digital model of a natural pipe sample using the finite element method.

[0048] Boundary conditions corresponding to the operational load values ​​of the MT process section are applied to the digital model of a full-scale pipe sample with a defect: loads (internal pressure p, bending moment M max ) and fixing to limit the displacements and rotation angles of the extreme points of the structure when performing the calculation.

[0049] Operational load values ​​can be taken from both design documentation for newly commissioned pipeline sections and from data from the dispatch control system for pipeline sections in operation.

[0050] A finite element mesh is applied to a digital model of a full-scale pipe sample with a defect.

[0051] The shape of the longitudinal weld seam in the digital model of a full-scale pipe sample with a defect (pos. 2) is constructed based on actual data on the geometric parameters of the longitudinal weld seam of the pipe based on measurements in its cross sections.

[0052] Create a digital model of a laboratory sample in the ANSYS software package using the finite element modeling method for subsequent uniaxial loading testing of a laboratory sample with a defect identical to the digital model of the pipe.

[0053] The initial data for creating a digital model of a laboratory specimen with a longitudinal weld and an applied artificial defect (pos. 2) and for manufacturing laboratory specimens are the following geometric characteristics of a laboratory pipe specimen with a defect: l is the working length of the specimen; b is the width of the specimen; H is the width of the specimen head; R is the radius of the mating part of the working part with the head of the specimen; W is the width of the defect; h is the depth of the defect, as well as the strength characteristics of the metal under study, determined during tensile tests.

[0054] A finite element mesh is applied to the digital model of the laboratory sample (pos. 2) for uniaxial loading.

[0055] The following boundary conditions are applied to the digital model of the laboratory sample (pos. 2): loads F (uniaxial tensile forces from the grips of the testing machine) and fastenings.

[0056] The forces F are selected for the digital model of the laboratory specimen (item 2), creating stresses at the defect apex under uniaxial loading equivalent to the stresses at the defect apex in the digital model of the full-scale pipe specimen with the defect (item 1). The selection of forces F from the grips is performed iteratively, with monitoring of the equivalent stresses in the defect area. The selection of forces F is considered complete when the maximum equivalent stresses at the defect apex in the digital model of the laboratory specimen become equal to the maximum equivalent stresses σ экв at the top of the defect of the digital model of a full-scale pipe sample with a defect in the technological section of the MT with operational loads.

[0057] Prediction of crack propagation (expected number of cycles to failure) is performed. The expected number of cycles to failure is calculated using the ANSYS Fatigue software package.

[0058] Crack growth prediction is carried out in stages.

[0059] Before the first stage of calculation, a defect (Fig. 2; Fig. 9) of width W and depth h is introduced into the digital model of the laboratory sample.

[0060] The necessary data for the calculation are entered: characteristics of cyclic loads, strength characteristics of the metal obtained as a result of tensile tests.

[0061] The criterion for the completion of each stage is the excess of the effective equivalent stresses over the elastic limit of the metal σ min the cross-sectional plane of a digital model of a laboratory specimen, coinciding with the plane of the defect. The zone of plastic deformation (pos. 3) of a section of the specimen cross-section is identified and measured, and the number of cycles to failure in this zone is determined (Fig. 8).

[0062] After processing the results, the depth h of the defect (pos. 2) in the digital model of the laboratory sample is increased by the value of the plastic deformation zone (pos. 4), the finite element mesh is rebuilt and the next stage calculation is performed.

[0063] Step-by-step modeling ends at the moment when the equivalent stresses in the cross-sectional plane of the digital model of the laboratory sample, coinciding with the plane of the defect, begin to exceed the value of the elastic limit of the metal σ m The number of cycles to failure determined at each stage is cumulative.

[0064] Then laboratory samples are made from a natural pipe sample, with the addition of artificial defects identical to the defects of the natural pipe sample (Fig. 9).

[0065] Each of the laboratory samples is a flat full-thickness pipe element with a thickness corresponding to the thickness of the pipe wall metal δ, a working length l, a width b, a width of the head of the sample H; with a mating radius of the working part with the head of the sample R and with the same geometry of the longitudinal weld seam of the pipe, with an artificial defect (pos. 1) applied by a milling cutter with a diameter of 50 mm and a width of 0.5 mm to a given depth h, identical to the defect of the full-scale pipe sample.

[0066] Laboratory specimens are tested for cyclic tension under uniaxial loading on a multi-purpose servo-hydraulic testing machine until failure with a maximum force in the F cycle, the value of which was determined during the selection of forces on a digital model of a laboratory specimen with a defect.

[0067] The calculation results and test results are compared.

[0068] To ensure the reliability of tests and eliminate the influence of heating of laboratory samples during testing on the final result, the loading frequency in all cyclic tests ensures that the temperature of laboratory samples does not exceed plus 40°C.

[0069] Tests are carried out until the destruction of laboratory samples in order to determine the residual life.

[0070] Example of the invention.

[0071] To implement the method, a process section of the main pipeline (MP) with a defect (pos. 1) was selected, followed by cutting out a full-scale sample of a pipe with a standard size of 820×10 mm from steel grade 17GS.

[0072] The geometric characteristics of a full-scale pipe sample with a defect and the geometric parameters of the longitudinal weld seam were measured.

[0073] Two samples of pipe metal were cut from a full-scale pipe sample and tensile tests were carried out, the strength characteristics of the pipe wall material (yield strength σ) were determined m =385 MPa, ultimate strength σ в, =620 MPa, relative elongation at break δ5=21.9%. It is worth noting that the number of pipe metal samples may be greater if this is provided for by regulatory documents on the rules for sampling, blanks, and samples.

[0074] The construction of a digital model of a full-scale sample of a pipe with a defect (pos. 1) was carried out based on the geometric characteristics of the full-scale sample of the pipe with a defect and the geometric parameters of the longitudinal weld seam in the ANSYS software package for finite element modeling.

[0075] A model of a longitudinal weld defect (pos. 1) was integrated into the digital model of a full-scale pipe sample.

[0076] The geometric characteristics of the full-scale sample of the pipe with a defect were used as the initial data for constructing a digital model of the full-scale sample of the pipe with a defect: the outer diameter of the pipe D н =820 mm, pipe wall thickness δ=10 mm (Fig. 1). Initial data for constructing the defect model: defect length L=1610 mm, defect width W=0.5 mm, defect depth h=4 mm, defect location on the full-scale pipe sample (Fig. 2). Geometric parameters of the longitudinal weld: height of the outer weld reinforcement, height of the inner weld reinforcement, offset of the axes of the outer and inner welds, width of the outer weld reinforcement, width of the inner weld reinforcement, edge offset, weld overlap.

[0077] After forming a digital model of a full-scale pipe sample with a defect, a finite element mesh was applied to it (Fig. 3).

[0078] The calculation of the stress-strain state in the defect area was carried out in a geometrically and physically nonlinear formulation with the application of maximum operating loads: pressure p and bending moment M изг In one of the cases considered, the pressure p=5.05 MPa and the bending moment M изг =920 kN m. The behavior of the material was described by an elastic-plastic model with a power law of hardening.

[0079] Based on the results of constructing a digital model of a full-scale pipe sample and applying loads in the ANSYS software package, the maximum equivalent stresses σ were determined экв (Fig. 4) in the defect region σ экв =700.09 MPa.

[0080] The creation of a digital model of a laboratory sample with a defect (Fig. 9) was carried out based on the geometric characteristics of the laboratory sample with a defect, the geometric parameters of the longitudinal weld seam in the ANSYS software package for finite element modeling and the strength characteristics of the metal under study, determined during tensile tests.

[0081] The following geometric characteristics were used to construct the digital model of the laboratory specimen: working length of the specimen l=155 mm, specimen width b=15 mm, specimen head width H=100 mm, radius of the mating of the working part with the specimen head R=125 mm; geometric dimensions of the longitudinal weld (height of the outer weld reinforcement, height of the inner weld reinforcement, offset of the axes of the outer and inner welds, width of the outer weld reinforcement, width of the inner weld reinforcement, edge offset, weld overlap), geometric dimensions of the defect: defect width W=0.5 mm, defect depth h=4 mm; strength characteristics of the pipe metal (yield strength σ т =385 MPa, ultimate strength σ в =620 MPa, relative elongation at break δ5=21.9%), equivalent stresses in the defect area σ экв =700.09 MPa, calculated at the previous stage.

[0082] To construct a digital model of a laboratory sample with a defect, the following operations were performed:

[0083] - a digital model of a laboratory sample was constructed using the finite element method software package;

[0084] - the construction of a finite element mesh was carried out on a digital model of a laboratory sample (Fig. 5);

[0085] - boundary conditions were applied: loads F (uniaxial tensile forces from the grips of the testing machine) and fastenings (to limit the movements and rotation angles of the extreme points of the laboratory sample when performing the calculation) to the digital model of the laboratory sample with the calculation of equivalent stresses in the defect area;

[0086] - the selection of forces F on the digital model of the laboratory specimen from the grips of the testing machine was performed, creating stresses in the defect area equivalent to the stresses in the digital model of the full-scale pipe specimen with the defect; the selection of forces F was carried out iteratively, with control of the equivalent stresses in the defect area; the selection of forces was considered complete when the maximum equivalent stresses in the defect area in the digital model of the laboratory specimen became equal to the maximum equivalent stresses in the defect area σ экв , obtained during the calculation of the stress-strain state of a full-scale pipe sample with a defect; during the selection to achieve maximum equivalent stresses σ экв =700.09 MPa, it was necessary to apply a force F=219 kN to the digital model of the laboratory sample;

[0087] - Fatigue crack propagation was predicted in a digital model of a laboratory specimen (estimated expected number of cycles to failure); fatigue crack propagation in a digital model of a laboratory specimen was predicted using fracture mechanics methods; crack size changes (propagation) in the digital model of the laboratory specimen were simulated, and the finite element mesh was rebuilt; the expected number of cycles to failure of the digital model of the laboratory specimen was calculated using the ANSYS Fatigue software package.

[0088] Crack growth prediction was carried out in stages.

[0089] Before the first stage of calculation, a defect of width W and depth h was introduced into the digital model of the laboratory sample.

[0090] Initial data for calculation: characteristics of cyclic loads, strength and fatigue characteristics of the material.

[0091] The criterion for the completion of each stage was the excess of the effective equivalent stresses over the elastic limit of the material in the section of the sample cross-section with a defect.

[0092] During the calculation at each stage, the zone of plastic deformation of the section of the sample was identified (Fig. 7) and the number of cycles before failure in this zone was determined (Fig. 8).

[0093] After processing the calculation results at the current stage, the dimensions of the defect in the digital model of the laboratory sample were increased by the size of the plastic deformation zone (pos. 3), the finite element mesh was rebuilt and the calculation for the next stage was carried out.

[0094] Step-by-step modeling ended at the moment when the equivalent stresses in the cross-sectional plane of the digital model of the laboratory sample, coinciding with the plane of the defect, begin to exceed the value of the elastic limit of the metal σ m The number of cycles to failure determined at each stage was added together.

[0095] Next, two identical laboratory specimens were manufactured from the full-scale pipe sample (Fig. 9). It is worth noting that the number of laboratory specimens is not limited to two and can be increased depending on the expected number of cycles before failure. A low number of cycles before failure indicates high operational loads on the MT process section, which may require more detailed study. On the other hand, increasing the number of laboratory specimens with a high expected number of cycles before failure will significantly increase the testing time.

[0096] Artificial defects identical to the digital model were applied to laboratory specimens (specimen #1; specimen #2). The cyclic load from the grips of the testing machine on the laboratory specimens was specified as the maximum axial tensile force per cycle F = 219 kN (uniaxial loading), at which the maximum equivalent stresses at the defect tip in the digital model of the laboratory specimen correspond to the maximum equivalent stresses σ экв at the defect tip in a digital model of a full-scale pipe sample with the defect. Laboratory samples were tested with an asymmetry coefficient of 0.1 on a multipurpose servohydraulic testing machine (HA500) from Zwick / Roell GmbH, Germany.

[0097] After completing the tests, the results shown in Table 1 were obtained.

[0098]

[0099] Tests of laboratory samples (sample No. 1; sample No. 2) showed that the developed digital model of the laboratory sample made it possible to fairly accurately predict the durability of pipes with defects, since the number of cycles before failure of each laboratory sample did not go beyond the range of the number of cycles before failure calculated in the developed digital model of laboratory samples.

[0100] The assessment of the residual life of pipes with defects, made on the basis of theoretical calculation, is confirmed by the results of cyclic tests under laboratory conditions with a uniaxial loading scheme of laboratory samples.

[0101] The developed digital model of a laboratory sample allows for the assessment of the residual life of pipes with defects and can be adapted for testing samples with defects in other pipeline elements.

Claims

1. A method for conducting resource testing of pipes with defects in laboratory conditions using the uniaxial loading method on samples, characterized by the following steps being performed sequentially: - select a process section of the main pipeline (MP) with a defect; - a full-scale sample of the pipe is cut out from the MT process section; - measure the geometric characteristics of a full-scale sample of a pipe with a defect and the geometric parameters of the longitudinal weld; - at least two samples of pipe metal are cut from a full-scale pipe sample for tensile testing; - determine the strength properties of the pipe metal by testing metal samples for tension; - create a digital model of a full-scale sample of a pipe with a defect based on the geometric characteristics of the full-scale sample of a pipe with a defect and the geometric parameters of the longitudinal weld; - calculate equivalent stresses σ экв at the top of the defect of the digital model of a natural pipe sample using the finite element method; - create a digital model of a laboratory sample of a pipe with a defect based on the geometric characteristics of the laboratory sample of a pipe with a defect and the geometric parameters of the longitudinal weld seam, the strength characteristics of the pipe metal samples using equivalent stresses σ экв at the top of the defect of the digital model of the natural pipe sample, calculated at the previous stage; - a selection of uniaxial tensile forces from the grips of the testing machine on a digital model of a laboratory sample is carried out, which create stresses at the top of the defect equivalent to the stresses at the top of the defect of the digital model of a full-scale pipe sample with a defect, while the selection of forces from the grips is carried out iteratively, with control of equivalent stresses σ эквin the defect area, and the selection of forces is considered complete when the maximum equivalent stresses σ экв at the top of the defect in the digital model of the laboratory sample become equal to the maximum equivalent stresses at the top of the defect in the digital model of the full-scale sample, under the action of loads corresponding to the internal pressure p and the bending moment M max technological section of MT; - calculate the expected number of cycles until the complete destruction of the digital model of the sample using the finite element method; - at least two laboratory samples are manufactured according to the geometric characteristics of the laboratory sample of a pipe with a defect by cutting it from a full-scale sample of a pipe with the application of an artificial defect identical to the defect of the full-scale sample of the pipe, wherein each laboratory sample is a flat full-thickness element of a pipe corresponding to the thickness of the pipe wall metal δ with identical geometric parameters of the longitudinal weld seam of the pipe; - at least two laboratory specimens are tested using the cyclic uniaxial loading method with an asymmetry coefficient of 0.1 until their failure with a maximum axial tensile force in a cycle, the value of which was determined during the selection of forces on a digital model of a specimen with a defect, while the tests using the uniaxial loading method are carried out ensuring that the temperature of the laboratory specimens is not higher than plus 40°C; - the residual life of the technological section of the MT with a defect is determined by comparing the results of calculations and the results of laboratory tests to determine the number of cycles until the complete destruction of the digital model of the laboratory sample and laboratory samples.

2. The method according to paragraph 1, characterized in that the geometric characteristics of the full-scale sample of the pipe with the defect are the outer diameter of the pipe D н , pipe wall thickness δ, defect length L, defect width W, defect depth h, defect location on a full-scale pipe sample.

3. The method according to paragraph 1, characterized in that the geometric characteristics of the laboratory sample of a pipe with a defect are the working length of the sample, the width of the sample b, the width of the head of the sample H, the radius of the mating of the working part with the head of the sample R, the width of the defect W, the depth of the defect h.

4. The method according to paragraph 1, characterized in that the geometric parameters of the longitudinal weld seam are the height of the reinforcement of the outer seam, the height of the reinforcement of the inner seam, the offset of the axes of the outer and inner seams, the width of the reinforcement of the outer seam, the width of the reinforcement of the inner seam, the offset of the edges, and the overlap of the seams.

5. The method according to paragraph 1, characterized in that the strength characteristics of the pipe metal samples are the yield strength σ т , ultimate strength σ в and relative elongation at break δ5.

6. The method according to paragraph 1, characterized in that a digital model of a full-scale sample of a pipe with a defect and a digital model of a laboratory sample are created in the ANSYS software package for finite element modeling.

7. The method according to paragraph 1, characterized in that the expected number of cycles before the destruction of the digital model of the laboratory sample is performed in the ANSYS Fatigue software package, taking into account the predicted change in the size of the defect, with the rebuilding of the finite element mesh.

Images