Heterogeneity and crack tip micro-damage coupled macrocrack propagation model research method

Abstract

The invention discloses a heterogeneity and crack tip micro-damage coupled macrocrack propagation model research method, and belongs to the technical field of oil and gas storage and transportation. Comprising the steps of establishing a large-span temperature difference working condition simulation experiment table; secondly, the large-span temperature difference working condition simulation experiment table in the first step is used for inducing a welding part to generate micro damage, a first batch of workpiece welding seam cracks are obtained, an electronic probe analyzer, a transmission electron microscope (TEM), an X-ray diffraction analyzer (XRD) and a field emission scanning electron microscope (FESEM) are used for observing the first batch of workpiece welding seam cracks, and a second batch of workpiece welding seam cracks are obtained; a microstructure observation result of the weld crack is obtained; 2, analyzing a microstructure observation result of the weld crack obtained in the step 2, constructing an algorithm of a Voronoi diagram in combination with a convex hull of a finite element crystal nucleus point set and a triangulation module, compiling a crystal growth model, and establishing a micromechanical model; a cohesive unit method is adopted, and the elasticity modulus, plasticity and damage parameters of a micromechanical model are set.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas storage and transportation, and in particular to a method for studying a macro crack propagation model of coupling heterogeneity with micro damage at the crack tip. Background Art

[0002] For high-pressure vessels serving in sour gas fields or gas fields in areas with large temperature differences between day and night, they will be affected by factors such as hydrogen permeation, thermal expansion and contraction, and fatigue. Combined with the cumulative damage and material asymptotic damage theory, the above factors can easily cause micro-damage to the welds of such high-pressure vessels and induce crack propagation, thus posing a safety hazard to the efficient and safe development of such gas fields.

[0003] Based on the "fitness for use" and "weakest link" principles, accurately determining whether in-service pressure vessels with weld crack defects can continue to be used safely under specified operating conditions is an essential requirement for ensuring the safe operation of pressure vessels and is also an engineering need. If the assessment results are too conservative, frequent repairs and replacements will affect the normal production of the gas field and cause economic losses; if the assessment results are too bold, allowing them to exist will leave safety hazards. Pressure vessels containing sour gases have higher manufacturing costs, which puts higher demands on maximum economic development. Therefore, how to improve the safety assessment accuracy of high-pressure vessels in the above environment has always been a technical bottleneck that has plagued the efficient and safe development of such gas fields.

[0004] Micro-damage is micron-to-nano-scale damage in the structure, including crystal defects, material performance degradation, and micron-scale cracks. From initiation to failure, cracks induced by micro-damage go through three stages: crack initiation, steady-state expansion, and unstable expansion. When the stress intensity factor K at the crack tip is greater than KIC (fracture criterion), the crack expands, leading to fracture failure. There are fruitful research results on the safety hazards faced by high-pressure vessels with crack defects. However, the existing research on the dynamic mechanism of micro-damage-induced crack growth is basically proposed for a certain type of metal material or a certain deformation stage, which cannot be universally applied. This paper proposes a research method for a macro crack growth model that couples heterogeneity with micro-damage at the crack tip, aiming to carry out the inversion of the evolution process of micro-damage-induced crack growth in welds under large-span temperature differences, and further clarify the dynamic mechanism of micro-damage-induced crack growth in welds under large-span temperature differences. Summary of the invention

[0005] The purpose of the present invention is to provide a method for studying a macro crack propagation model that couples heterogeneity with micro damage at the crack tip, so as to solve the problems raised in the above background technology.

[0006] In view of the above problems, the technical solution proposed by the present invention is: A method for studying a macro crack growth model coupled with heterogeneity and crack tip micro-damage includes the following steps: Step 1: Establish a large-span temperature difference working condition simulation test bench; Step 2: Use the large-span temperature difference working condition simulation test bench in step 1 to induce micro-damage in the welded parts, obtain the first batch of workpiece weld cracks, and use electron probe analyzer, transmission electron microscope (TEM), X-ray diffraction analyzer (XRD) and field emission scanning electron microscope (FESEM) to observe the first batch of workpiece weld cracks to obtain the microstructure observation results of the weld cracks; Step 3: Analyze the microstructure observation results of the weld crack obtained in step 2, combine the convex hull and triangulation modules of the finite element crystal core point set, construct the algorithm of the Voronoi diagram, compile the crystal growth model, and establish the micromechanical model; Adopting the cohesive unit method, by setting the elastic modulus, plasticity, and damage parameters of the micromechanical model, the heterogeneity of the material is restored, and an Abaqus plug-in is written to realize the insertion and assignment of the customized cohesive layer of any grid model. Based on the Monte-Carlo random assignment method, a heterogeneous finite element model is constructed. Combine micromechanical models, finite element models, and fracture mechanics to establish a three-dimensional crack growth prediction model; Step 4: Conduct failure simulation tests using the large-span temperature difference working condition simulation test bench in step 1 to induce weld cracks in the second batch of workpieces under different conditions; The crack propagation of the weld seams of the second batch of workpieces was monitored by acoustic emission, the crack parameters of the weld seams of the second batch of workpieces were detected by ultrasonic testing, and the stress changes of the cracks in the weld seams of the second batch of workpieces were monitored by stress and strain sensors. Fracture failure analysis was performed to verify the stress distribution law, residual strength calculation, and safety assessment method. Combined with the verification of stress distribution law, residual strength calculation and safety assessment method, the three-dimensional crack propagation prediction model obtained in step three is further revised.

[0007] As a preferred technical solution of the present invention, the large-span temperature difference working condition simulation test bench in step one includes a fatigue testing machine, the working chamber of the fatigue pressure testing machine is divided into a low temperature zone and a high temperature zone, the outer cover of the fatigue pressure testing machine is provided with a nitrogen protective shell, and the nitrogen protective shell is connected to a nitrogen discharge port, the large-span temperature difference working condition simulation test bench includes a fatigue testing machine and also includes an acid gas tank, a constant temperature and pressure gas buffer tank, a pair of reheaters, a liquid nitrogen tank, and a vaporizer, liquid nitrogen is stored in the liquid nitrogen tank, the liquid nitrogen tank is connected to the vaporizer, one of the reheaters is connected to the vaporizer, and at the same time is connected to the nitrogen protective shell through a regulating valve 1, and is connected to the constant temperature and pressure gas buffer tank through a regulating valve 2, the liquid nitrogen tank is connected to the constant temperature and pressure gas buffer tank through a regulating valve 3, and the constant temperature and pressure gas buffer tank is connected to the low temperature zone through a regulating valve 5.

[0008] As a preferred technical solution of the present invention, acid gas is stored in the acid gas tank, another reheater is connected to the acid gas tank, and is connected to the constant temperature and pressure gas buffer tank through a regulating valve 4, and the constant temperature and pressure gas buffer tank is connected to the high temperature zone through a regulating valve 6.

[0009] Specifically, a solenoid valve is installed at the nitrogen discharge port to control the discharge of nitrogen in the nitrogen protection shell. A temperature control loop is set between the constant temperature and pressure gas buffer tank and regulating valve 2, regulating valve 3, and regulating valve 4 to control the temperature in the constant temperature and pressure gas buffer tank, and a temperature control loop is also set between the nitrogen protection shell and regulating valve 1 to control the temperature in the nitrogen protection shell. The constant temperature and pressure gas buffer tank, the nitrogen protection shell, a pair of reheaters, a vaporizer, an acid gas tank, and a liquid nitrogen tank are all connected by pipelines, and regulating valve 1, regulating valve 2, regulating valve 3, regulating valve 4, regulating valve 5, and regulating valve 6 are all installed on the pipeline.

[0010] As a preferred technical solution of the present invention, the transmission electron microscope (TEM) in the step 2 is used to test and analyze the microstructure of the micro-area before and after the cracks appear in the first batch of workpiece welds; the X-ray diffraction analyzer (XRD) is used to analyze the relevant composition and relative content of the crack parts of the first batch of workpiece welds; the field emission scanning electron microscope (FESEM) is used to test the microstructure and morphology of the crack parts of the first batch of workpiece welds, and characterize the number, morphology, size, and spatial arrangement of the organizational grains and crystal defects in the micro-damaged parts of the welded parts.

[0011] As a preferred technical solution of the present invention, the different conditions in step four include different gas ratios, different pressures applied by different mixed gases to the second batch of workpieces, and different experimental temperatures. The different conditions in step four are used to obtain weld cracks of the second batch of workpieces at different positions and weld cracks of the second batch of workpieces of different types.

[0012] Specifically, the ratio between the acid gas and liquid nitrogen of the large-span temperature difference working condition simulation test bench is changed to adjust the hydrogen flux, the pressure of the acid gas and liquid nitrogen of the large-span temperature difference working condition simulation test bench is changed to change the gas pressure of the second batch of workpieces, and the temperature of the acid gas and liquid nitrogen of the large-span temperature difference working condition simulation test bench is changed to change the experimental temperature.

[0013] Compared with the prior art, the beneficial effects of the present invention are: the research method of the macro crack propagation model of coupling heterogeneity and crack tip micro damage, constructs a macro crack propagation model of coupling heterogeneity and crack tip micro damage with the help of finite element numerical simulation software, and combines the weld crack failure simulation test to carry out the inversion of the evolution process of weld micro damage induced crack propagation under large span temperature difference, and further clarifies the dynamic mechanism of weld micro damage induced crack propagation under large span temperature difference. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a general method block diagram of the research method of the macro crack propagation model coupling of heterogeneity and crack tip micro damage disclosed in the embodiment of the present invention; Figure 2 A diagram of the construction process of a macro crack growth model of coupling heterogeneity with micro damage at the crack tip in a research method of a macro crack growth model of coupling heterogeneity with micro damage at the crack tip disclosed in an embodiment of the present invention; Figure 3 A schematic diagram of the structure of an experimental platform for a method for studying a macro crack propagation model coupled with heterogeneity and crack tip micro-damage disclosed in an embodiment of the present invention; Figure 4 The present invention discloses a flow chart of a weld crack failure simulation experiment for a method for studying a macro crack propagation model of coupling heterogeneity with micro damage at the crack tip disclosed in an embodiment of the present invention. DETAILED DESCRIPTION

[0015] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions 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 are within the scope of protection of the present invention.

[0016] See also Figure 1 - Figure 4 The present invention provides a technical solution: a method for studying a macro crack propagation model of coupling heterogeneity and crack tip micro damage, comprising the following steps: Step 1: Establish a large-span temperature difference working condition simulation test bench; Step 2: Use the large-span temperature difference working condition simulation test bench in step 1 to induce micro-damage in the welded parts, obtain the first batch of workpiece weld cracks, and use electron probe analyzer, transmission electron microscope (TEM), X-ray diffraction analyzer (XRD) and field emission scanning electron microscope (FESEM) to observe the first batch of workpiece weld cracks to obtain the microstructure observation results of the weld cracks; Step 3: Analyze the microstructure observation results of the weld crack obtained in step 2, combine the convex hull and triangulation modules of the finite element crystal core point set, construct the algorithm of the Voronoi diagram, compile the crystal growth model, and establish the micromechanical model; Adopting the cohesive unit method, by setting the elastic modulus, plasticity, and damage parameters of the micromechanical model, the heterogeneity of the material is restored, and an Abaqus plug-in is written to realize the insertion and assignment of the customized cohesive layer of any grid model. Based on the Monte-Carlo random assignment method, a heterogeneous finite element model is constructed. The micromechanical model, finite element model and fracture mechanics are combined to establish a three-dimensional crack propagation prediction model.

[0017] An embodiment of the present invention is further characterized in that the working chamber of the fatigue pressure tester is divided into a low temperature zone and a high temperature zone, the outer cover of the fatigue pressure tester is provided with a nitrogen protective shell, the nitrogen protective shell is connected with a nitrogen discharge port, and the large-span temperature difference working condition simulation test bench includes a fatigue tester and also includes an acid gas tank, a constant temperature and pressure gas buffer tank, a pair of reheaters, a liquid nitrogen tank, and a vaporizer. Liquid nitrogen is stored in the liquid nitrogen tank, the liquid nitrogen tank is connected to the vaporizer, one of the reheaters is connected to the vaporizer, and at the same time, it is connected to the nitrogen protective shell through a regulating valve 1, and is connected to the constant temperature and pressure gas buffer tank through a regulating valve 2, the liquid nitrogen tank is connected to the constant temperature and pressure gas buffer tank through a regulating valve 3, and the constant temperature and pressure gas buffer tank is connected to the low temperature zone through a regulating valve 5.

[0018] In one embodiment of the present invention, further, acid gas is stored in the acid gas tank, another reheater is connected to the acid gas tank, and is connected to the constant temperature and pressure gas buffer tank through the regulating valve 4, and the constant temperature and pressure gas buffer tank is connected to the high temperature zone through the regulating valve 6.

[0019] In one embodiment of the present invention, further, a solenoid valve is installed at the nitrogen discharge port to control the discharge of nitrogen in the nitrogen protection shell, a temperature control loop is set between the constant temperature and pressure gas buffer tank and regulating valve 2, regulating valve 3, and regulating valve 4 to control the temperature in the constant temperature and pressure gas buffer tank, and a temperature control loop is also set between the nitrogen protection shell and regulating valve 1 to control the temperature in the nitrogen protection shell, the constant temperature and pressure gas buffer tank, the nitrogen protection shell, a pair of reheaters, a vaporizer, an acid gas tank, and a liquid nitrogen tank are all connected by pipelines, and regulating valve 1, regulating valve 2, regulating valve 3, regulating valve 4, regulating valve 5, and regulating valve 6 are all installed on the pipeline.

[0020] In one embodiment of the present invention, further, the transmission electron microscope (TEM) in step 2 is used to test and analyze the microstructure of the micro-area before and after the cracks appear in the first batch of workpiece welds; the X-ray diffraction analyzer (XRD) is used to analyze the relevant composition and relative content of the crack parts of the first batch of workpiece welds; the field emission scanning electron microscope (FESEM) is used to test the microstructure and morphology of the crack parts of the first batch of workpiece welds, and characterize the number, morphology, size, and spatial arrangement of the organizational grains and crystal defects in the micro-damaged parts of the welded parts.

[0021] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions 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 are within the scope of protection of the present invention.

[0022] See also Figure 1 - Figure 4 The present invention provides a technical solution: a method for studying a macro crack propagation model of coupling heterogeneity and crack tip micro-damage, comprising the following steps: Step 1: Conduct failure simulation tests using a large-span temperature difference working condition simulation test bench to induce weld cracks in the second batch of workpieces under different conditions; The crack propagation of the weld seams of the second batch of workpieces was monitored by acoustic emission, the crack parameters of the weld seams of the second batch of workpieces were detected by ultrasonic testing, and the stress changes of the cracks in the weld seams of the second batch of workpieces were monitored by stress and strain sensors. Fracture failure analysis was performed to verify the stress distribution law, residual strength calculation, and safety assessment method. Combined with the verification of stress distribution law, residual strength calculation and safety assessment method, the three-dimensional crack propagation prediction model obtained in step three is further revised.

[0023] An embodiment of the present invention is used. Further, the large-span temperature difference working condition simulation test bench in step one includes a fatigue testing machine, the working chamber of the fatigue pressure testing machine is divided into a low temperature zone and a high temperature zone, the outer cover of the fatigue pressure testing machine is provided with a nitrogen protective shell, the nitrogen protective shell is connected with a nitrogen discharge port, the large-span temperature difference working condition simulation test bench includes the fatigue testing machine and also includes an acid gas tank, a constant temperature and pressure gas buffer tank, a pair of reheaters, a liquid nitrogen tank, and a vaporizer. Liquid nitrogen is stored in the liquid nitrogen tank, the liquid nitrogen tank is connected to the vaporizer, one of the reheaters is connected to the vaporizer, and at the same time is connected to the nitrogen protective shell through a regulating valve 1, and is connected to the constant temperature and pressure gas buffer tank through a regulating valve 2. An embodiment of the present invention is used. Further, the liquid nitrogen tank is connected to the constant temperature and pressure gas buffer tank through a regulating valve 3, and the constant temperature and pressure gas buffer tank is connected to the low temperature zone through a regulating valve 5.

[0024] In one embodiment of the present invention, further, acid gas is stored in the acid gas tank, another reheater is connected to the acid gas tank, and is connected to the constant temperature and pressure gas buffer tank through the regulating valve 4, and the constant temperature and pressure gas buffer tank is connected to the high temperature zone through the regulating valve 6.

[0025] In one embodiment of the present invention, further, a solenoid valve is installed at the nitrogen discharge port to control the discharge of nitrogen in the nitrogen protection shell, a temperature control loop is set between the constant temperature and pressure gas buffer tank and regulating valve 2, regulating valve 3, and regulating valve 4 to control the temperature in the constant temperature and pressure gas buffer tank, and a temperature control loop is also set between the nitrogen protection shell and regulating valve 1 to control the temperature in the nitrogen protection shell, the constant temperature and pressure gas buffer tank, the nitrogen protection shell, a pair of reheaters, a vaporizer, an acid gas tank, and a liquid nitrogen tank are all connected by pipelines, and regulating valve 1, regulating valve 2, regulating valve 3, regulating valve 4, regulating valve 5, and regulating valve 6 are all installed on the pipeline.

[0026] In one embodiment of the present invention, further, the different conditions in step four include different gas ratios, different pressures applied by mixed gases to the second batch of workpieces, and different experimental temperatures. The different conditions in step four are used to obtain weld cracks of the second batch of workpieces at different positions and weld cracks of the second batch of workpieces of different types.

[0027] According to an embodiment of the present invention, further, the ratio between the acid gas and the liquid nitrogen is changed to adjust the hydrogen flux, the pressure of the acid gas and the liquid nitrogen is changed to change the gas pressure of the second batch of workpieces, and the temperature of the acid gas and the liquid nitrogen is changed to change the experimental temperature.

Claims

1. A method for studying a macro crack growth model that couples heterogeneity with micro damage at the crack tip, characterized in that: The following steps are involved: Step 1: Establish a large-span temperature difference working condition simulation test bench; Step 2: Use the large-span temperature difference working condition simulation test bench in step 1 to induce micro-damage in the welded parts, obtain the first batch of workpiece weld cracks, and use electron probe analyzer, transmission electron microscope (TEM), X-ray diffraction analyzer (XRD) and field emission scanning electron microscope (FESEM) to observe the first batch of workpiece weld cracks to obtain the microstructure observation results of the weld cracks; Step 3: Analyze the microstructure observation results of the weld crack obtained in step 2, combine the convex hull and triangulation modules of the finite element crystal core point set, construct the algorithm of the Voronoi diagram, compile the crystal growth model, and establish the micromechanical model; Adopting the cohesive unit method, by setting the elastic modulus, plasticity, and damage parameters of the micromechanical model, the heterogeneity of the material is restored, and an Abaqus plug-in is written to realize the insertion and assignment of the customized cohesive layer of any grid model. Based on the Monte-Carlo random assignment method, a heterogeneous finite element model is constructed. Combine micromechanical models, finite element models, and fracture mechanics to establish a three-dimensional crack growth prediction model; Step 4: Conduct failure simulation tests using the large-span temperature difference working condition simulation test bench in step 1 to induce weld cracks in the second batch of workpieces under different conditions; The crack propagation of the weld seams of the second batch of workpieces was monitored by acoustic emission, the crack parameters of the weld seams of the second batch of workpieces were detected by ultrasonic testing, and the stress changes of the cracks in the weld seams of the second batch of workpieces were monitored by stress and strain sensors. Fracture failure analysis was performed to verify the stress distribution law, residual strength calculation, and safety assessment method. Combined with the verification of stress distribution law, residual strength calculation and safety assessment method, the three-dimensional crack propagation prediction model obtained in step three is further revised.

2. The method for studying a macro crack growth model of coupling heterogeneity and crack tip micro damage according to claim 1 is characterized in that: The large-span temperature difference working condition simulation test bench in step one includes a fatigue testing machine, the working chamber of the fatigue pressure testing machine is divided into a low temperature zone and a high temperature zone, the outer cover of the fatigue pressure testing machine is provided with a nitrogen protective shell, the nitrogen protective shell is connected with a nitrogen discharge port, the large-span temperature difference working condition simulation test bench includes a fatigue testing machine and also includes an acid gas tank, a constant temperature and pressure gas buffer tank, a pair of reheaters, a liquid nitrogen tank, and a vaporizer, liquid nitrogen is stored in the liquid nitrogen tank, the liquid nitrogen tank is connected to the vaporizer, one of the reheaters is connected to the vaporizer, and at the same time, it is connected to the nitrogen protective shell through a regulating valve 1, and is connected to the constant temperature and pressure gas buffer tank through a regulating valve 2, the liquid nitrogen tank is connected to the constant temperature and pressure gas buffer tank through a regulating valve 3, and the constant temperature and pressure gas buffer tank is connected to the low temperature zone through a regulating valve 5.

3. The method for studying a macro crack growth model of coupling heterogeneity and crack tip micro damage according to claim 2 is characterized in that: The acid gas tank stores acid gas, the other reheater is connected to the acid gas tank, and is connected to the constant temperature and pressure gas buffer tank through a regulating valve 4, and the constant temperature and pressure gas buffer tank is connected to the high temperature zone through a regulating valve 6.

4. The method for studying a macro crack growth model of coupling heterogeneity and crack tip micro damage according to claim 1, characterized in that: The transmission electron microscope (TEM) in the step 2 is used to test and analyze the microstructure of the micro-area before and after the cracks appear in the first batch of workpiece welds; the X-ray diffraction analyzer (XRD) is used to analyze the relevant composition and relative content of the crack parts of the first batch of workpiece welds; the field emission scanning electron microscope (FESEM) is used to test the microstructure and morphology of the crack parts of the first batch of workpiece welds, and characterize the number, morphology, size, and spatial arrangement of the organizational grains and crystal defects in the micro-damaged parts of the welded parts.

5. The method for studying a macro crack growth model coupled with heterogeneity and crack tip micro damage according to claim 1, characterized in that: The different conditions in step four include different gas ratios, different pressures applied by mixed gases to the second batch of workpieces, and different experimental temperatures. The different conditions in step four are used to obtain weld cracks of the second batch of workpieces at different positions and weld cracks of the second batch of workpieces of different types.

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