Gas flexible pipes are critical multi-layered equipment for offshore oil and gas development.Under high pressure conditions,small molecular components of natural gas dissolve into the polymer inner liner of the flexib...Gas flexible pipes are critical multi-layered equipment for offshore oil and gas development.Under high pressure conditions,small molecular components of natural gas dissolve into the polymer inner liner of the flexible pipes and further diffuse into the annular space,incurring annular pressure build-up and/or production of acidic environment,which poses serious challenges to the structure and integrity of the flexible pipes.Gas permeation in pipes is a complex phenomenon governed by various factors such as internal pressure and temperature,annular structure,external temperature.In a long-distance gas flexible pipe,moreover,gas permeation exhibits non-uniform features,and the gas permeated into the annular space flows along the metal gap.To assess the complex gas transport behavior in long-distance gas flexible pipes,a mathematical model is established in this paper considering the multiphase flow phenomena inside the flexible pipes,the diffusion of gas in the inner liner,and the gas seepage in the annular space under varying permeable properties of the annulus.In addition,the effect of a variable temperature is accounted.A numerical calculation method is accordingly constructed to solve the coupling mathematical equations.The annular permeability was shown to significantly influence the distribution of annular pressure.As permeability increases,the annular pressure tends to become more uniform,and the annular pressure at the wellhead rises more rapidly.After annular pressure relief followed by shut-in,the pressure increase follows a convex function.By simulating the pressure recovery pattern after pressure relief and comparing it with test results,we deduce that the annular permeability lies between 123 and 512 m D.The results help shed light upon assessing the annular pressure in long distance gas flexible pipes and thus ensure the security of gas transport in the emerging development of offshore resources.展开更多
To improve the drill pipe fracture failure phenomenon in deflecting drills with ultra-short radius flexible drill pipes,this study establishes a mechanical model of a deflecting drill with an ultra-short radius flexib...To improve the drill pipe fracture failure phenomenon in deflecting drills with ultra-short radius flexible drill pipes,this study establishes a mechanical model of a deflecting drill with an ultra-short radius flexible drill pipe,numerically simulates the mechanical characteristics of the flexible drill pipe under the conventional drilling process using the finite element analysis method,performs mechanical performance tests on the flexible drill pipe,and optimizes and improves its structure.The results show that,with the gradual increase in the bending angle of the flexible drill pipe unit section,the upper drilling pressure of the flexible drill pipe unit section decreases rapidly and its friction increases approximately linearly.The tensile strength of the optimized ultra-short radius flexible drill pipe is increased by 24.7%,and the minimum threshold of its torsional strength is doubled.This effectively improves the overall strength of the ultra-short radius flexible drill pipe and provides a theoretical basis for downhole drilling stability studies of flexible drill pipes.展开更多
The unbonded flexible pipe of eight layers, in which all the layers except the carcass layer are assumed to have isotropic properties, has been analyzed. Specifically, the carcass layer shows the orthotropic character...The unbonded flexible pipe of eight layers, in which all the layers except the carcass layer are assumed to have isotropic properties, has been analyzed. Specifically, the carcass layer shows the orthotropic characteristics. The effective elastic moduli of the carcass layer have been developed in terms of the influence of deformation to stiffness. With consideration of the effective elastic moduli, the structure can be properly analyzed. Also the relative movements of tendons and relative displacements of wires in helical armour layer have been investigated. A three-dimensional nonlinear finite element model has been presented to predict the response of flexible pipes under axial force and torque. Further, the friction and contact of interlayer have been considered. Comparison between the finite element model and experimental results obtained in literature has been given and discussed, which might provide practical and technical support for the application of unbonded flexible pipes.展开更多
The flexible pipe bend can not only reduce the structural vibration and fluid noise in pipeline, but also realize the flexible connection of a horizontal line and a vertical line and compensate the displacement of thr...The flexible pipe bend can not only reduce the structural vibration and fluid noise in pipeline, but also realize the flexible connection of a horizontal line and a vertical line and compensate the displacement of three dimensions produced by the shock or vibration of pipeline in the special situations. Up to now, little attention has been paid to study the flexible pipe bend applied in the pipeline of medium or high pressure, because no appropriate framework materials can be used to reinforce it which must endure the burst pressure higher than 10 MPa. The investigation shows that it is possible to produce the flexible pipe bend of medium or high pressure if such fibers with high performance as Kevlar fibers are used to be its reinforced materials. However, its structural designing theory, manufacturing technology and measuring techniques aren't yet perfect and systematic, which leads to the instability of the performance of products. Furthermore, few references about its research can be seen. Therefore, it is necessary to systematically and thoroughly develop the structural designing theory, manufacture technology and measuring techniques of flexible pipe bend.展开更多
This paper presents an analytical scheme for predicting the collapse strength of a flexible pipe, which considers the structural interaction between relevant layers. The analytical results were compared with a FEA mod...This paper presents an analytical scheme for predicting the collapse strength of a flexible pipe, which considers the structural interaction between relevant layers. The analytical results were compared with a FEA model and a number of test data, and showed reasonably good agreement. The theoretical analysis showed that the pressure armor layer enhanced the strength of the carcass against buckling, though the barrier weakened this effect. The collapse strength of pipe was influenced by many factors such as the inner radius of the pipe, the thickness of the layers and the mechanical properties of the materials. For example, an increase in the thickness of the barrier will increase contact pressure and in turn reduce the critical pressure.展开更多
As key components connecting offshore floating production platforms and subsea imports, offshore flexible pipes play significant roles in oil, natural gas, and water injection. It is found that torsional failure is on...As key components connecting offshore floating production platforms and subsea imports, offshore flexible pipes play significant roles in oil, natural gas, and water injection. It is found that torsional failure is one of the failure modes of flexible pipes during transportation and laying. In this paper, a theoretical model(TM) of a flexible pipe section mechanics is established, in which the carcass layer and the pressure armor layer are equivalent to the orthogonal anisotropic layers due to its complex cross-section structure. The calculation results of the TM are consistent with those of a finite element model(FEM), which can accurately describe the torsional response of the flexible pipe.Subsequently, the TM and FEM are used to discuss the influence of boundary conditions on the torsional response.The structure of the flexible pipe is stable when twisted counterclockwise. However, limiting the top axial displacement can improve the axial and radial instability of the tensile armor layer when twisted clockwise. Finally, it is recommended that the flexible pipe can be kept under top fixation during service or installation to avoid torsional failure.展开更多
A pipe model with a mass ratio（mass/displaced mass） of 4.30 was tested to investigate the vortex-induced vibrations of submarine pipeline spans near the seabed.The pipe model was designed as a bending stiffness-domi...A pipe model with a mass ratio（mass/displaced mass） of 4.30 was tested to investigate the vortex-induced vibrations of submarine pipeline spans near the seabed.The pipe model was designed as a bending stiffness-dominated beam.The gap ratios（gap to diameter ratio） at the pipe ends were 4.0,6.0,and 8.0.The flow velocity was systematically varied in the 0-16.71 nondimensional velocity range based on the first natural frequency.The mode transition between the first and the second mode as the flow velocity increases was investigated.At various transition flow velocities,the research indicates that the peak frequencies with respect to displacement are not identical along the pipe,nor the frequencies associated with the peak of the amplitude spectra for the first four modes as well.The mode transition is associated with a continuous change in the amplitude,but there＇s a jump in frequency,and a gradual process along the pipe length.展开更多
Steel wire wound reinforced flexible pipe in this study mainly consists of multiple anisotropic steel wire wound reinforcement layers and multiple isotropic rubber layers.Based on 3D anisotropic elastic theory,the ana...Steel wire wound reinforced flexible pipe in this study mainly consists of multiple anisotropic steel wire wound reinforcement layers and multiple isotropic rubber layers.Based on 3D anisotropic elastic theory,the analytic solutions of stresses and elastic deformations of steel wire wound reinforced rubber flexible pipe under internal pressure are presented.As the adjacent reinforcement layers with wound angle have different radii,the single reinforcement layer shows the effect of tensile-shear coupling.Moreover,the static loading test results of steel wire wound reinforced rubber flexible pipe under internal pressure are basically coincided with the calculated values by present method.展开更多
Axial structural damping behavior induced by internal friction and viscoelastic properties of polymeric layers may have an inevitable influence on the global analysis of flexible pipes.In order to characterize this ph...Axial structural damping behavior induced by internal friction and viscoelastic properties of polymeric layers may have an inevitable influence on the global analysis of flexible pipes.In order to characterize this phenomenon and axial mechanical responses,a full-scale axial tensile experiment on a complex flexible pipe is conducted at room temperature,in which oscillation forces at different frequencies are applied on the sample.The parameters to be identified are axial strains which are measured by three kinds of instrumentations:linear variable differential transformer,strain gauge and camera united particle-tracking technology.The corresponding plots of axial force versus axial elongation exhibit obvious nonlinear hysteretic relationship.Consequently,the loss factor related to the axial structural damping behavior is found,which increases as the oscillation loading frequency grows.The axial strains from the three measurement systems in the mechanical experiment indicate good agreement,as well as the values of the equivalent axial stiffness.The damping generated by polymeric layers is relatively smaller than that caused by friction forces.Therefore,it can be concluded that friction forces maybe dominate the axial structural damping,especially on the conditions of high frequency.展开更多
The carcass layer of flexible pipe comprises a large-angle spiral structure with a complex interlocked stainless steel cross-section profile, which is mainly used to resist radial load. With the complex structure of t...The carcass layer of flexible pipe comprises a large-angle spiral structure with a complex interlocked stainless steel cross-section profile, which is mainly used to resist radial load. With the complex structure of the carcass layer, an equivalent simplified model is used to study the mechanical properties of the carcass layer. However, the current equivalent carcass model only considers the elastic deformation, and this simplification leads to huge errors in the calculation results. In this study, radial compression experiments were carried out to make the carcasses to undergo plastic deformation. Subsequently, a residual neural network based on the experimental data was established to predict the load-displacement curves of carcasses with different inner diameter in plastic states under radial compression.The established neural network model’s high precision was verified by experimental data, and the influence of the number of input variables on the accuracy of the neural network was discussed. The conclusion shows that the residual neural network model established based on the experimental data of the small-diameter carcass layer can predict the load-displacement curve of the large-diameter carcass layer in the plastic stage. With the decrease of input data, the prediction accuracy of residual network model in plasticity stage will decrease.展开更多
Three kinds of models based on the same flexible pipe with 8 layers have been separately created to investigate the effects of different modeling approaches on numerical simulation results of finite element(FE)models ...Three kinds of models based on the same flexible pipe with 8 layers have been separately created to investigate the effects of different modeling approaches on numerical simulation results of finite element(FE)models for unbonded flexible pipes.Then the mechanical property of the unbonded flexible pipe under tension,torsion and bending load has been analyzed and compared via ABAQUS software on the basis of three created models.The research shows that different modeling methods of flexible pipes make a great difference in the results.Especially,modeling simplifications of the carcass and pressure armor have a great impact on the accuracy of the results.Model 3,in which the carcass is simulated by spiral isot ropic shell and other layers are Simula ted by solid element,possesses good adaptability,which has been proved by comparing the experiment data and other models.This paper can offer a reference for the FE modeling methods,selection and mechanical property analysis of unbonded flexible pipe.展开更多
The instability of the tensile armor wire of flexible pipes is a failure mode associated with deep and ultra-deep water applications. Real compressive forces acting on the pipe are necessary to trigger this process. T...The instability of the tensile armor wire of flexible pipes is a failure mode associated with deep and ultra-deep water applications. Real compressive forces acting on the pipe are necessary to trigger this process. The loss of stability may be divided into two distinct processes, according to the main direction of the wire＇s displacement： radial or lateral instability. This study aims at proposing a numerical tool for predicting lateral and radial critical buckling loads for the tensile armor wires of flexible pipes. A simple finite element model, based on springs and beams elements, was developed in ABAQUS~ to deal with this problem in an efficient and reliable manner. A parametric study was conducted concerning the behavior of the critical load when the laying angle, the initial curvature and the total pipe length are varied. The results were consistent with previously published literature data and analytical expressions, proving its applicability to pipe engineering projects. It also has the advantage of approaching the problem three-dimensionally, which allows further modelling modifications, such as including friction effects.展开更多
Flexible composite pipes are advantageous in ultra high strength,high modulus,pH and corrosion resistance and light weight,but there are still some hidden safety troubles because they are poorer in thermostable capaci...Flexible composite pipes are advantageous in ultra high strength,high modulus,pH and corrosion resistance and light weight,but there are still some hidden safety troubles because they are poorer in thermostable capacity.Therefore,test samples of flexible composite pipes were prepared with high-temperature polythene(PE-RT)as the neck bush and aramid fiber as the reinforcement layer.Experimental study was conducted by using HPHT vessel and differential thermal scanner for different working conditions,different temperatures,whole-pipe pressure-bearing capacity and 1000 h viability.It is shown by the environmental compatibility test that high temperature has little effect on the weight,Vicat softening temperature,mechanical properties and structures of neck bush PE-RT,but exerts an obvious effect on the tensility and wholepipe water pressure blasting of the reinforcement aramid fiber.Besides,the drop of whole-pipe pressure-bearing capacity is caused by deformation and breaking of aramid fibers when the reinforcement layer is under the force of internal pressure.Finally,disorientation and crystallization of molecular thermal motion occur with the rise of temperature,so amorphous orientation reduces,crystallinity factor and crystalline orientation factor increase gradually,thus,disorientation of macromolecular chains increases and tensile strength decreases.It is concluded that this type of flexible composite pipe can smoothly pass 1000 h viability test.And it is recommended that it be used in the situations with temperature not higher than 95℃and internal pressure not higher than 4 MPa.展开更多
With the development of cities and the advancement of urbanization in China, the underground pipeline system in cities is becoming more and more complicated. Functional defects and structural defects caused by disrepa...With the development of cities and the advancement of urbanization in China, the underground pipeline system in cities is becoming more and more complicated. Functional defects and structural defects caused by disrepair and geological uneven settlement of urban water supply facilities are increasingly prominent. The contradiction between the population growth brought by the rapid development of the city and the high-quality and high-value development requirements for the environment has gradually increased, making it more difficult to excavate and repair. Compared with excavation repair, trenchless repair has the characteristics of no impact on traffic, no damage to the environment, short construction period, good construction safety and significant social benefits. Through the summary of flexible lining technology, reference and technical support are provided for the implementation of subsequent similar projects. The trenchless repair and renovation engineering technology of municipal underground pipelines has been recognized by people due to its small interference to the ground, high construction speed, low comprehensive cost, good safety, low carbon emissions and other reasons, and has been gradually introduced and popularized in the field of municipal pipe network construction, renovation and repair.展开更多
Nonbonded flexible pipes consist of polymer materials that experience stress relaxation at high temperatures,which ultimately affects the sealing performance of end sealing systems.To assess stress relaxation curves u...Nonbonded flexible pipes consist of polymer materials that experience stress relaxation at high temperatures,which ultimately affects the sealing performance of end sealing systems.To assess stress relaxation curves under varying temperatures and pre-strains,this paper conducts both tensile and stress relaxation tests on PVDF materials.To describe the stress relaxation characteristics of these materials,the Prony series is utilized.In order to identify the parameters of the series,the paper employs the Levenberg-Marquardt method of nonlinear regression.A finite element model is established to verify the accuracy of the parameter identification method.Subsequently,the paper establishes a two-dimensional axisymmetric finite element model of the sealing system in the end fitting,while taking into account fluid pressure inside the pipeline using a pressure penetration method.The impact of stress relaxation on the sealing performance is then discussed.Finally,the paper alters the coefficients of the Prony series to explore their significance on the sealing performance of the sealing system.展开更多
Marine unbonded flexible pipes serve as the most essential equipment in offshore oil and gas exploration and exploitation.Axial compressive loads during installation or in service in the complex marine environment usu...Marine unbonded flexible pipes serve as the most essential equipment in offshore oil and gas exploration and exploitation.Axial compressive loads during installation or in service in the complex marine environment usually lead to buckling failure.A flexible pipe is a composite structure with multiple functional layers,of which the tensile armor layer plays a key role with regard to the response of the pipe subjected to axial loads.In this paper,a simplified three-dimensional finite element model is developed,focusing on the tensile layer and replacing the carcass layer,pressure sheath layer,and pressure armor layer by a cylindrical rigid body to reduce computational expense.By using this model,the buckling failure modes of the tensile armor layer(in particular the birdcaging phenomenon)are analyzed.Several key parameters that affect the stability of the flexible pipe under axial compression and torsion are emphasized,and their effects on its axial and torsional stiffness are compared and discussed.The results show that both the lay angle of the steel wires and the interlayer friction coefficient have a significant influence on the axial and torsional stiffness of the pipe,whereas the damaged length of the outer sheath has virtually no effect.展开更多
基金supported by the Natural Science Research Project of Guangling College of Yangzhou University,China (ZKZD18004)General Program of Natural Science Research in Higher Education Institutions of Jiangsu Province,China (20KJD430006)。
文摘Gas flexible pipes are critical multi-layered equipment for offshore oil and gas development.Under high pressure conditions,small molecular components of natural gas dissolve into the polymer inner liner of the flexible pipes and further diffuse into the annular space,incurring annular pressure build-up and/or production of acidic environment,which poses serious challenges to the structure and integrity of the flexible pipes.Gas permeation in pipes is a complex phenomenon governed by various factors such as internal pressure and temperature,annular structure,external temperature.In a long-distance gas flexible pipe,moreover,gas permeation exhibits non-uniform features,and the gas permeated into the annular space flows along the metal gap.To assess the complex gas transport behavior in long-distance gas flexible pipes,a mathematical model is established in this paper considering the multiphase flow phenomena inside the flexible pipes,the diffusion of gas in the inner liner,and the gas seepage in the annular space under varying permeable properties of the annulus.In addition,the effect of a variable temperature is accounted.A numerical calculation method is accordingly constructed to solve the coupling mathematical equations.The annular permeability was shown to significantly influence the distribution of annular pressure.As permeability increases,the annular pressure tends to become more uniform,and the annular pressure at the wellhead rises more rapidly.After annular pressure relief followed by shut-in,the pressure increase follows a convex function.By simulating the pressure recovery pattern after pressure relief and comparing it with test results,we deduce that the annular permeability lies between 123 and 512 m D.The results help shed light upon assessing the annular pressure in long distance gas flexible pipes and thus ensure the security of gas transport in the emerging development of offshore resources.
基金supported by Open Fund of Technology Innovation Center for Directional Drilling Engineering,Ministry of Natural Resources./Innovation Base for Directional Drilling Engineering,Geological Society of China(-No.KF202302)the Geological Survey projects of China Geological Survey(No.DD20221681)+1 种基金Open Found Projects of Sinopec Key Laboratory of Geothermal Resources Exploitation and Utilizatio(No.36650000-23-ZC0607-0054)Open Research Fund Program of Key Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitoring(Ministry of Education),Central South University(2023YSJS06).
文摘To improve the drill pipe fracture failure phenomenon in deflecting drills with ultra-short radius flexible drill pipes,this study establishes a mechanical model of a deflecting drill with an ultra-short radius flexible drill pipe,numerically simulates the mechanical characteristics of the flexible drill pipe under the conventional drilling process using the finite element analysis method,performs mechanical performance tests on the flexible drill pipe,and optimizes and improves its structure.The results show that,with the gradual increase in the bending angle of the flexible drill pipe unit section,the upper drilling pressure of the flexible drill pipe unit section decreases rapidly and its friction increases approximately linearly.The tensile strength of the optimized ultra-short radius flexible drill pipe is increased by 24.7%,and the minimum threshold of its torsional strength is doubled.This effectively improves the overall strength of the ultra-short radius flexible drill pipe and provides a theoretical basis for downhole drilling stability studies of flexible drill pipes.
基金supported by the "111" Project of China (Grant No. B07019)State Key Laboratory of Ocean Engineeringof Shanghai Jiao Tong University (Grant No. 1008)the Fundamental Research Funds for the Central University
文摘The unbonded flexible pipe of eight layers, in which all the layers except the carcass layer are assumed to have isotropic properties, has been analyzed. Specifically, the carcass layer shows the orthotropic characteristics. The effective elastic moduli of the carcass layer have been developed in terms of the influence of deformation to stiffness. With consideration of the effective elastic moduli, the structure can be properly analyzed. Also the relative movements of tendons and relative displacements of wires in helical armour layer have been investigated. A three-dimensional nonlinear finite element model has been presented to predict the response of flexible pipes under axial force and torque. Further, the friction and contact of interlayer have been considered. Comparison between the finite element model and experimental results obtained in literature has been given and discussed, which might provide practical and technical support for the application of unbonded flexible pipes.
文摘The flexible pipe bend can not only reduce the structural vibration and fluid noise in pipeline, but also realize the flexible connection of a horizontal line and a vertical line and compensate the displacement of three dimensions produced by the shock or vibration of pipeline in the special situations. Up to now, little attention has been paid to study the flexible pipe bend applied in the pipeline of medium or high pressure, because no appropriate framework materials can be used to reinforce it which must endure the burst pressure higher than 10 MPa. The investigation shows that it is possible to produce the flexible pipe bend of medium or high pressure if such fibers with high performance as Kevlar fibers are used to be its reinforced materials. However, its structural designing theory, manufacturing technology and measuring techniques aren't yet perfect and systematic, which leads to the instability of the performance of products. Furthermore, few references about its research can be seen. Therefore, it is necessary to systematically and thoroughly develop the structural designing theory, manufacture technology and measuring techniques of flexible pipe bend.
文摘This paper presents an analytical scheme for predicting the collapse strength of a flexible pipe, which considers the structural interaction between relevant layers. The analytical results were compared with a FEA model and a number of test data, and showed reasonably good agreement. The theoretical analysis showed that the pressure armor layer enhanced the strength of the carcass against buckling, though the barrier weakened this effect. The collapse strength of pipe was influenced by many factors such as the inner radius of the pipe, the thickness of the layers and the mechanical properties of the materials. For example, an increase in the thickness of the barrier will increase contact pressure and in turn reduce the critical pressure.
基金financially supported by the Natural Science Starting Project of SWPU (Grant No. 2022QHZ002)Sichuan Natural Science Foundation Youth Fund Project (Grant No. 2023NSFC0918)。
文摘As key components connecting offshore floating production platforms and subsea imports, offshore flexible pipes play significant roles in oil, natural gas, and water injection. It is found that torsional failure is one of the failure modes of flexible pipes during transportation and laying. In this paper, a theoretical model(TM) of a flexible pipe section mechanics is established, in which the carcass layer and the pressure armor layer are equivalent to the orthogonal anisotropic layers due to its complex cross-section structure. The calculation results of the TM are consistent with those of a finite element model(FEM), which can accurately describe the torsional response of the flexible pipe.Subsequently, the TM and FEM are used to discuss the influence of boundary conditions on the torsional response.The structure of the flexible pipe is stable when twisted counterclockwise. However, limiting the top axial displacement can improve the axial and radial instability of the tensile armor layer when twisted clockwise. Finally, it is recommended that the flexible pipe can be kept under top fixation during service or installation to avoid torsional failure.
基金Supported by the National Natural Science Foundation of China（No.41176072） the Scientific Research Fund of Hunan Provincial Education Department（No.12C0030）+1 种基金 the Program for Hu’nan Province Key Laboratory of Water,Sediment Sciences and Flood Hazard Prevention（No.2012SS07） the National Natural Science Foundation for Youth of China（No.51109018）
文摘A pipe model with a mass ratio（mass/displaced mass） of 4.30 was tested to investigate the vortex-induced vibrations of submarine pipeline spans near the seabed.The pipe model was designed as a bending stiffness-dominated beam.The gap ratios（gap to diameter ratio） at the pipe ends were 4.0,6.0,and 8.0.The flow velocity was systematically varied in the 0-16.71 nondimensional velocity range based on the first natural frequency.The mode transition between the first and the second mode as the flow velocity increases was investigated.At various transition flow velocities,the research indicates that the peak frequencies with respect to displacement are not identical along the pipe,nor the frequencies associated with the peak of the amplitude spectra for the first four modes as well.The mode transition is associated with a continuous change in the amplitude,but there＇s a jump in frequency,and a gradual process along the pipe length.
基金the National Natural Science Foundation of China (No. 50439010)
文摘Steel wire wound reinforced flexible pipe in this study mainly consists of multiple anisotropic steel wire wound reinforcement layers and multiple isotropic rubber layers.Based on 3D anisotropic elastic theory,the analytic solutions of stresses and elastic deformations of steel wire wound reinforced rubber flexible pipe under internal pressure are presented.As the adjacent reinforcement layers with wound angle have different radii,the single reinforcement layer shows the effect of tensile-shear coupling.Moreover,the static loading test results of steel wire wound reinforced rubber flexible pipe under internal pressure are basically coincided with the calculated values by present method.
基金the support from the National Natural Science Foundation of China(Youth Program)(Grant No.51809276)the National Key Research and Development Plan of China(Grant No.2018YFC0310504)CNPq-National Council of Scientific and Technological Development(Grant No.302380/2013-2)。
文摘Axial structural damping behavior induced by internal friction and viscoelastic properties of polymeric layers may have an inevitable influence on the global analysis of flexible pipes.In order to characterize this phenomenon and axial mechanical responses,a full-scale axial tensile experiment on a complex flexible pipe is conducted at room temperature,in which oscillation forces at different frequencies are applied on the sample.The parameters to be identified are axial strains which are measured by three kinds of instrumentations:linear variable differential transformer,strain gauge and camera united particle-tracking technology.The corresponding plots of axial force versus axial elongation exhibit obvious nonlinear hysteretic relationship.Consequently,the loss factor related to the axial structural damping behavior is found,which increases as the oscillation loading frequency grows.The axial strains from the three measurement systems in the mechanical experiment indicate good agreement,as well as the values of the equivalent axial stiffness.The damping generated by polymeric layers is relatively smaller than that caused by friction forces.Therefore,it can be concluded that friction forces maybe dominate the axial structural damping,especially on the conditions of high frequency.
基金financially supported by the National Key R&D Program of China (2021YFA1003501)the National Natural Science Foundation of China (No.U1906233,11732004)the Fundamental Research Funds for the Central Universities (DUT20ZD213,DUT20LAB308)。
文摘The carcass layer of flexible pipe comprises a large-angle spiral structure with a complex interlocked stainless steel cross-section profile, which is mainly used to resist radial load. With the complex structure of the carcass layer, an equivalent simplified model is used to study the mechanical properties of the carcass layer. However, the current equivalent carcass model only considers the elastic deformation, and this simplification leads to huge errors in the calculation results. In this study, radial compression experiments were carried out to make the carcasses to undergo plastic deformation. Subsequently, a residual neural network based on the experimental data was established to predict the load-displacement curves of carcasses with different inner diameter in plastic states under radial compression.The established neural network model’s high precision was verified by experimental data, and the influence of the number of input variables on the accuracy of the neural network was discussed. The conclusion shows that the residual neural network model established based on the experimental data of the small-diameter carcass layer can predict the load-displacement curve of the large-diameter carcass layer in the plastic stage. With the decrease of input data, the prediction accuracy of residual network model in plasticity stage will decrease.
基金the National Natural Science Foundation of China(Nos.11627802 and 51709118)the China Postdoctoral Science Foundation(No.2017M612669)+2 种基金the Science and Technology Program of Guangzhou(No.201804010482)the Fundamental Research Funds for the Central Universities of China(No.2017BQ089)the Fund of State Key Laboratory of Ocean Engineering of Shanghai Jiao Tong University(No.1708)
文摘Three kinds of models based on the same flexible pipe with 8 layers have been separately created to investigate the effects of different modeling approaches on numerical simulation results of finite element(FE)models for unbonded flexible pipes.Then the mechanical property of the unbonded flexible pipe under tension,torsion and bending load has been analyzed and compared via ABAQUS software on the basis of three created models.The research shows that different modeling methods of flexible pipes make a great difference in the results.Especially,modeling simplifications of the carcass and pressure armor have a great impact on the accuracy of the results.Model 3,in which the carcass is simulated by spiral isot ropic shell and other layers are Simula ted by solid element,possesses good adaptability,which has been proved by comparing the experiment data and other models.This paper can offer a reference for the FE modeling methods,selection and mechanical property analysis of unbonded flexible pipe.
文摘The instability of the tensile armor wire of flexible pipes is a failure mode associated with deep and ultra-deep water applications. Real compressive forces acting on the pipe are necessary to trigger this process. The loss of stability may be divided into two distinct processes, according to the main direction of the wire＇s displacement： radial or lateral instability. This study aims at proposing a numerical tool for predicting lateral and radial critical buckling loads for the tensile armor wires of flexible pipes. A simple finite element model, based on springs and beams elements, was developed in ABAQUS~ to deal with this problem in an efficient and reliable manner. A parametric study was conducted concerning the behavior of the critical load when the laying angle, the initial curvature and the total pipe length are varied. The results were consistent with previously published literature data and analytical expressions, proving its applicability to pipe engineering projects. It also has the advantage of approaching the problem three-dimensionally, which allows further modelling modifications, such as including friction effects.
文摘Flexible composite pipes are advantageous in ultra high strength,high modulus,pH and corrosion resistance and light weight,but there are still some hidden safety troubles because they are poorer in thermostable capacity.Therefore,test samples of flexible composite pipes were prepared with high-temperature polythene(PE-RT)as the neck bush and aramid fiber as the reinforcement layer.Experimental study was conducted by using HPHT vessel and differential thermal scanner for different working conditions,different temperatures,whole-pipe pressure-bearing capacity and 1000 h viability.It is shown by the environmental compatibility test that high temperature has little effect on the weight,Vicat softening temperature,mechanical properties and structures of neck bush PE-RT,but exerts an obvious effect on the tensility and wholepipe water pressure blasting of the reinforcement aramid fiber.Besides,the drop of whole-pipe pressure-bearing capacity is caused by deformation and breaking of aramid fibers when the reinforcement layer is under the force of internal pressure.Finally,disorientation and crystallization of molecular thermal motion occur with the rise of temperature,so amorphous orientation reduces,crystallinity factor and crystalline orientation factor increase gradually,thus,disorientation of macromolecular chains increases and tensile strength decreases.It is concluded that this type of flexible composite pipe can smoothly pass 1000 h viability test.And it is recommended that it be used in the situations with temperature not higher than 95℃and internal pressure not higher than 4 MPa.
文摘With the development of cities and the advancement of urbanization in China, the underground pipeline system in cities is becoming more and more complicated. Functional defects and structural defects caused by disrepair and geological uneven settlement of urban water supply facilities are increasingly prominent. The contradiction between the population growth brought by the rapid development of the city and the high-quality and high-value development requirements for the environment has gradually increased, making it more difficult to excavate and repair. Compared with excavation repair, trenchless repair has the characteristics of no impact on traffic, no damage to the environment, short construction period, good construction safety and significant social benefits. Through the summary of flexible lining technology, reference and technical support are provided for the implementation of subsequent similar projects. The trenchless repair and renovation engineering technology of municipal underground pipelines has been recognized by people due to its small interference to the ground, high construction speed, low comprehensive cost, good safety, low carbon emissions and other reasons, and has been gradually introduced and popularized in the field of municipal pipe network construction, renovation and repair.
基金the National Natural Science Foundation of China[Grant No.52088102,52001208,52111530135]Joint Funds of the National Natural Science Foundation of China[Grant No.U19B2013]+2 种基金Young Elite Scientists Sponsorship Program by CAST[Grant No.2020QNRC001]Chenguang Program of Shanghai Education Development Foundation and Shanghai Municipal Education Commission[Grant No.21CGA15,19CG10]Natural Science Foundation of Shanghai[Grant No.21ZR1434500,22ZR1434100].
文摘Nonbonded flexible pipes consist of polymer materials that experience stress relaxation at high temperatures,which ultimately affects the sealing performance of end sealing systems.To assess stress relaxation curves under varying temperatures and pre-strains,this paper conducts both tensile and stress relaxation tests on PVDF materials.To describe the stress relaxation characteristics of these materials,the Prony series is utilized.In order to identify the parameters of the series,the paper employs the Levenberg-Marquardt method of nonlinear regression.A finite element model is established to verify the accuracy of the parameter identification method.Subsequently,the paper establishes a two-dimensional axisymmetric finite element model of the sealing system in the end fitting,while taking into account fluid pressure inside the pipeline using a pressure penetration method.The impact of stress relaxation on the sealing performance is then discussed.Finally,the paper alters the coefficients of the Prony series to explore their significance on the sealing performance of the sealing system.
基金supported by the National Natural Science Foun-dation of China(No.51904262)China Postdoctoral Science Foundation(43XB3793XB).
文摘Marine unbonded flexible pipes serve as the most essential equipment in offshore oil and gas exploration and exploitation.Axial compressive loads during installation or in service in the complex marine environment usually lead to buckling failure.A flexible pipe is a composite structure with multiple functional layers,of which the tensile armor layer plays a key role with regard to the response of the pipe subjected to axial loads.In this paper,a simplified three-dimensional finite element model is developed,focusing on the tensile layer and replacing the carcass layer,pressure sheath layer,and pressure armor layer by a cylindrical rigid body to reduce computational expense.By using this model,the buckling failure modes of the tensile armor layer(in particular the birdcaging phenomenon)are analyzed.Several key parameters that affect the stability of the flexible pipe under axial compression and torsion are emphasized,and their effects on its axial and torsional stiffness are compared and discussed.The results show that both the lay angle of the steel wires and the interlayer friction coefficient have a significant influence on the axial and torsional stiffness of the pipe,whereas the damaged length of the outer sheath has virtually no effect.
