CN-121997624-A - Design method of dense-phase carbon dioxide pipeline composite material crack stopper

CN121997624ACN 121997624 ACN121997624 ACN 121997624ACN-121997624-A

Abstract

The invention discloses a design method of a dense-phase carbon dioxide pipeline composite material crack stopper, which comprises the following steps of S1, selecting a sample steel pipe, determining a crack steady-state expansion crack tip opening angle CTOA in the steel pipe, S2, determining a steel pipe crack stopper critical CTOAc, S3, establishing a finite element model, adopting five-layer entity units to grid the pipeline, adopting a cohesive force unit for a crack expansion path, S4, establishing a pressure attenuation model, S5, loading pressure by a two-step method, simulating the pressure of a crack tip, S6, determining cohesive force parameters, taking the cohesive force parameters as finite element model parameters, S7, determining a crack stopper model, setting a crack stopper criterion, and outputting CTOAa by finite element calculation, S8, determining the crack stopper criterion, and completing the design of the crack stopper. The design method of the dense-phase carbon dioxide pipeline composite material crack stopper solves the problem that the dense-phase carbon dioxide pipeline with small caliber of OD508 and below cannot be timely crack-stopped after being cracked.

Inventors

LI HE
WANG JUN
LI SHENGNAN

Assignees

中国石油天然气集团有限公司
中国石油集团工程材料研究院有限公司

Dates

Publication Date: 20260508
Application Date: 20241108

Claims (9)

1. The design method of the dense-phase carbon dioxide pipeline composite material crack stopper is characterized by comprising the following steps of: s1, selecting a sample steel pipe, and determining a crack steady-state expansion crack tip opening angle CTOA in the steel pipe through a DWTT experiment; S2, determining a steel pipe crack-stopping critical CTOAc by adopting a double-sample method; s3, establishing a finite element model, namely adopting five layers of entity units to grid-divide a pipeline by using a general program, and adopting a cohesive force unit for a crack propagation path; s4, establishing a pressure attenuation model in the crack propagation process; S5, loading pressure according to a pressure attenuation model in a two-step method, and simulating the pressure behind the crack tip; s6, when CTOA obtained through calculation is matched with CTOA determined through a test, determining cohesive force parameters, and taking the cohesive force parameters as finite element model parameters; s7, determining a composite material crack stopper model, setting a composite material crack stopper criterion, and carrying out finite element calculation output CTOAa; s8, determining a crack stopper criterion to complete the design of the composite material crack stopper.
2. The method for designing a dense phase carbon dioxide pipeline composite crack stopper according to claim 1, wherein the specific process of S1 is as follows: s1.1, selecting a steel pipe, and obtaining a stress-strain curve of the steel pipe through a steel pipe transverse round bar sample test; S1.2, carrying out a DWTT experiment, collecting load-displacement and load-time curves of a hammer head, and carrying out high-speed shooting; S1.3, determining the linear period time t 1 and t 2 of the steel pipe, and calculating CTOA by using the opening displacement at the position 2mm behind the crack tip in the period of t 1 ～t 2 through high-speed shooting and the stress strain curve of the steel pipe.
3. The design method of the dense-phase carbon dioxide pipeline composite material crack stopper is characterized in that the specific process of S2 is that a drop hammer sample is processed according to GB/T8363-2018 standard, a herringbone notch sample is adopted, 2 samples with the width of 76.2mm and the width of 43mm are respectively processed, drop hammer tearing experiments are carried out, hammering energy is collected in the drop hammer tearing experiment process, energy S c required by plastic deformation per unit volume of a region around a fracture surface is determined according to a formula (1), and a steel pipe crack stopping critical CTOA c is calculated according to a formula (2) and a formula (3); σ a ＝0,72(σ y +σ u ) (3); Wherein Et is hammering energy, A is ligament area, L is ligament length, rc is energy per unit area and represents energy required for forming a new interface, sc is energy required for plastic deformation per unit volume of a region around a fracture surface, sigma y is steel pipe yield strength, and sigma u is steel pipe tensile strength.
4. The method for designing the dense-phase carbon dioxide pipeline composite material crack stopper according to claim 1, wherein the specific process of the step S3 is that ABAQUS software is selected to axially model a pipeline part with the length being five times the diameter of the pipeline, an 8-node entity unit is used to model the pipeline, five layers of units are used to model the whole pipeline thickness, an 8-node cohesive unit with the initial thickness being zero is used to model a cohesive area, the cohesive unit has zero thickness, and the circumferential length is 0.25mm.
5. The method for designing a dense phase carbon dioxide pipeline composite crack stopper according to claim 1, wherein the specific process of S4 is to build a pressure decay model in the crack propagation process, in which the internal pressure is divided into a moving crack tip front area and a crack tip rear area, for the moving crack tip front area, assuming that the pressure is equal to the crack tip pressure, i.e. ignoring the decay from full pressure to the crack front steady state crack tip pressure, the crack tip pressure is equal to the carbon dioxide component saturation pressure, and for the area where the flap opening occurs behind the crack tip, the pressure decay is expressed as an exponential function of the circumferential variation, as shown in formula (4): Wherein, when θ is less than 75 °, c=0.0082 θ+0.48, when θ is greater than or equal to 75 °, c=1, when θ is less than 80 °, n= -2.6lnθ+11, and when θ is greater than or equal to 80 °, n=1.
6. The method for designing a dense phase carbon dioxide pipeline composite crack stopper according to claim 1, wherein the specific process of S5 is as follows: Firstly, under the condition of not introducing cracks, adopting ABAQUS software to initially pressurize in a quasi-static mode; And secondly, after the initial pressurization is finished, introducing an initial crack and introducing a pressurized deformed pipeline, performing dynamic analysis by using an ABAQUS software Explicit solver module, reducing the internal pressure to the steady-state crack tip pressure Ptip, and simulating the pressure behind the crack tip by adopting a pressure attenuation model in S4.
7. The method for designing the dense-phase carbon dioxide pipeline composite material crack stopper according to claim 1, wherein the specific process of S6 is that after the loading of pressure is finished by a two-step method, continuously adjusting cohesive force unit parameters, calculating a crack tip opening angle under the specified crack tip pressure, calculating CTOA by using an opening displacement at a position of 2mm behind the crack tip, increasing CTOA value when the crack is initially expanded, gradually reducing and stabilizing CTOA value, comparing CTOA value after steady-state expansion with crack steady-state expansion crack tip opening angle CTOA obtained by test in S1 until the two are equal, and selecting cohesive force unit parameters at the moment as finite element model parameters; The cohesive force unit adopts a bilinear traction force-separation amount curve, and cohesive energy is calculated according to a formula (5); Wherein G is cohesive energy, σ m is maximum traction force, δ c is critical separation amount, σ m ＝2.8σ y ;σ y is steel pipe yield strength, and initial slope of cohesive unit is 100 times of steel pipe elastic modulus, namely k=210×10 11 .
8. The method for designing the dense-phase carbon dioxide pipeline composite material crack stopper is characterized in that the composite material crack stopper adopts a superelastic material model based on Marlow strain energy potential, the crack stopper and a pipeline adopt a surface-surface contact mode, a first surface is selected as the outer surface of the pipeline, a second surface is selected as the inner surface of the crack stopper, tangential behaviors are set to be friction-free, normal behaviors are set to be hard contact, and the failure behaviors of the superelastic material model single fiber based on Marlow strain energy potential in the stretching process are adopted, so that the output CTOAa is calculated through a finite element model.
9. The method for designing the dense-phase carbon dioxide pipeline composite material crack stopper according to claim 1, wherein the specific process of S8 is that CTOAa of the crack determined by S3-S7 entering the crack stopper is compared with a steel pipe crack stopper critical CTOAc determined by S2, and when CTOAa is less than CTOAc, the crack stopper realizes crack stopper, and the composite material crack stopper is designed.

Description

Design method of dense-phase carbon dioxide pipeline composite material crack stopper Technical Field The invention belongs to the technical field of fracture control of carbon dioxide conveying pipelines, and particularly relates to a design method of a dense-phase carbon dioxide pipeline composite material crack stopper. Background Compared with natural gas, dense-phase carbon dioxide has a long decompression wave platform (saturation pressure), so that the pressure at the tip of a crack cannot be released, and the crack is easy to propagate for a long time to cause huge loss of personnel and property. Once the dense-phase carbon dioxide pipeline is cracked, the high-pressure gas in the pipeline cannot be immediately emptied, and a pressure reducing wave is generated from the breaking point to two sides and propagates to the far end. Because the gas decompression wave speed is lower than the crack expansion speed, the crack tip can keep a continuous high-stress state, and the crack can also continuously expand at a high speed, so that the ductile crack of the gas transmission pipeline can be expanded in a long range. The long-range expansion of cracks in dense-phase carbon dioxide pipelines can cause huge disasters and losses, so that the pipelines must be ensured to be capable of timely crack arrest once cracked. The existing full-size blasting test results show that for a high design coefficient CO 2 pipeline, the crack is difficult to stop by means of self toughness, and the problem is a bottleneck problem which seriously threatens the pipeline safety and restricts the application of a carbon dioxide pipeline. Disclosure of Invention The invention aims to provide a design method of a dense-phase carbon dioxide pipeline composite material crack stopper, which solves the problem that a dense-phase carbon dioxide pipeline with small caliber of OD508 and below cannot be timely crack-stopped after being cracked. The technical scheme adopted by the invention is that the design method of the dense-phase carbon dioxide pipeline composite material crack stopper comprises the following steps: s1, selecting a sample steel pipe, and determining a crack steady-state expansion crack tip opening angle CTOA in the steel pipe through a DWTT experiment; S2, determining a steel pipe crack-stopping critical CTOAc by adopting a double-sample method; s3, establishing a finite element model, namely adopting five layers of entity units to grid-divide a pipeline by using a general program, and adopting a cohesive force unit for a crack propagation path; s4, establishing a pressure attenuation model in the crack propagation process; S5, loading pressure according to a pressure attenuation model in a two-step method, and simulating the pressure behind the crack tip; s6, when CTOA obtained through calculation is matched with CTOA determined through a test, determining cohesive force parameters, and taking the cohesive force parameters as finite element model parameters; s7, determining a composite material crack stopper model, setting a composite material crack stopper criterion, and carrying out finite element calculation output CTOAa; s8, determining a crack stopper criterion to complete the design of the composite material crack stopper. The invention is also characterized in that: the specific process of S1 is as follows: s1.1, selecting a steel pipe, and obtaining a stress-strain curve of the steel pipe through a steel pipe transverse round bar sample test; S1.2, carrying out a DWTT experiment, collecting load-displacement and load-time curves of a hammer head, and carrying out high-speed shooting; S1.3, determining the linear period time t 1 and t 2 of the steel pipe, and calculating CTOA by using the opening displacement at the position 2mm behind the crack tip in the period of t 1～t2 through high-speed shooting and the stress strain curve of the steel pipe. The concrete process of S2 is that a drop hammer sample is processed according to GB/T8363-2018 standard, a herringbone notch sample is adopted, 2 samples with the width of 76.2mm and the width of 43mm are respectively processed, drop hammer tearing experiments are carried out, hammering energy is collected in the drop hammer tearing experiment process, energy S c required by plastic deformation per unit volume of the area around a fracture surface is determined according to a formula (1), and a steel pipe fracture stopping critical CTOA c is calculated according to a formula (2) and a formula (3); σa＝0.72(σy+σu) (3); Wherein Et is hammering energy, A is ligament area, L is ligament length, rc is energy per unit area and represents energy required for forming a new interface, sc is energy required for plastic deformation per unit volume of a region around a fracture surface, sigma y is steel pipe yield strength, and sigma u is steel pipe tensile strength. The specific process of the S3 is that ABAQUS software is selected to carry out axial modeling on a pipeline part w