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external pressure
ABSTRACT The external pressure collapse and propagation buckling of 8-inch submarine pipeline with design pressure of 56MPa are analyzed by 3-D finite element method in this paper (ABAQUS 6.14-4). The results show that the finite element analyses results are almost the same as analytical results using the criteria in DNVGL-ST-F101 2017. The propagation buckling criteria is limited to pipeline within 15
ABSTRACT Submarine pipelines can get damaged in various ways. An important failure mode is collapse. In the deep sea, the hydrostatic pressure is very large and the threat of said failure exists. There are prospects for pipelines in water depths of up to—at least—3,700 m. A pipeline requires a very thick wall to cope with such, hostile environment. This means that D/t, the diameter-to-wall-thickness ratio, must be low. The analytical limit-state equations included in DNV-ST-F101, a prevailing design standard for submarine pipeline systems, do not work well for pipe with extremely thick walls. Collapse-pressure predictions are increasingly conservative for lower D/t. By following the standard, pipelines operating in ultra-deep water may be over-dimensioned. This can culminate in manufacturing requirements that adversely affect project economics or threaten the technical feasibility altogether. This paper proposes an improved analytical framework for calculating the collapse pressure. Like the DNV model, the proposed model reflects the fundamental underlying and interacting physics of material yielding and geometric instability. It has been found that the collapse resistance of pipe with extremely thick walls (roughly D/t ≤ 15) is underestimated when using the DNV formulation. On the other hand, the capacity of pipe with slightly thinner walls (about 15 < D/t ≤ 40) could be overpredicted. The latter may occur if cold-formed line-pipe joints have not been subjected to some form of heat treatment after forming—for instance, via a coating process. To improve consistency between the predictive model and finite- element analysis, the analytical model has been extended to account for behaviours that were not yet included: triaxiality of stress and plastic bifurcation. The result is an elegant set of equations that can be used to evaluate the collapse pressure. Although the focus of this study was thick-walled pipe, the improvements lead to better collapse-pressure predictions for pipe with thinner walls, too.
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- Information Technology > Modeling & Simulation (0.54)
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Behavior of Buried Subsea Gas Pipeline Using Vector Form Intrinsic Finite Element Method
Li, Zhenmian (State Key Laboratory of Hydraulic Engineering Simulation and Safety, Tianjin University, Tianjin / Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration Shanghai) | Yu, Yang (State Key Laboratory of Hydraulic Engineering Simulation and Safety, Tianjin University, Tianjin / Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration Shanghai) | Cheng, Siyuan (State Key Laboratory of Hydraulic Engineering Simulation and Safety, Tianjin University, Tianjin / Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration Shanghai) | Liu, Xin (State Key Laboratory of Hydraulic Engineering Simulation and Safety, Tianjin University, Tianjin / Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration Shanghai) | You, Yaofeng (State Key Laboratory of Hydraulic Engineering Simulation and Safety, Tianjin University, Tianjin / Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration Shanghai) | Chen, Yang (State Key Laboratory of Hydraulic Engineering Simulation and Safety, Tianjin University, Tianjin / Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration Shanghai) | Xu, Lixin (State Key Laboratory of Hydraulic Engineering Simulation and Safety, Tianjin University, Tianjin / Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration Shanghai)
ABSTRACT Long-distance pipelines often inevitably run through seismic faults which may result in great threats to pipeline safety, such as twist deformation, wrinkling and tensile rupture. Buckling behavior of buried subsea gas pipeline under a strike-slip fault was investigated in this paper using the vector form intrinsic finite element (VFIFE) method. A special nonlinear soil spring model was developed for the VFIFE shell elements and numerical strategies were proposed to solve the multifold nonlinearities of geometric, elastoplastic material, and self-contact collision. Two different pressure conditions, the pressurized pipeline and the unpressurized pipeline, were considered respectively as the initial states. Effects of the crossing angles and the diameter-thickness ratios on buckling modes and axial strains were discussed. The results shows that the bending deformation of subsea pipeline is lateral buckling with two bends on both sides of the fault plane. For buckling failure judgement, the maximum flattening parameter is more suitable for the unpressurized pipeline while the maximum tensile strain for the pressurized pipeline. The unpressurized pipeline is more prone to fail with local collapse and buckling propagation. For thick pipelines, the deformations are dominated by the bending caused by the seismic fault and the main failure pattern is a dent of the compression side on the bends which even develop into a self-contact collision of the inner wall. For thin pipelines, local collapse and buckling propagation are induced by a small fault displacement and dominated by the external pressure. Both parallel and orthometric buckling propagation are observed. Whether the pressurized or unpressurized pipeline, a smaller crossing angle leads to more serious lateral deformations so that the critical fault displacement is smaller. Several design suggestions for offshore pipeline considering seismic faults are proposed. The results can be used to guide the seismic design and buckling prevention research of subsea pipeline crossing seismic faults.
Experimental Observations on Collapse Mechanisms of Faceted Subsea Pipeline
Alrsai, Mahmoud (School of Engineering, Al-Hussein Bin Talal University) | Karampour, Hassan (Griffith School of Engineering and Built Environment, Griffith University) | Alsanat, Husam (School of Engineering, Al-Hussein Bin Talal University)
ABSTRACT This study investigates the collapse mechanisms and capacity of the faceted pipe against the conventional pipe under external hydrostatic pressure. The experimental protocol is comprised of additively manufactured (3D-printed) faceted and conventional titanium pipes (Ti6Al4V-0406) tested inside a 30MPa hyperbaric chamber. A finite element analysis (FEA) is presented and is validated against the experimental results. Using the validated FE model, the major geometric parameters affecting the collapse capacity of faceted pipe were investigated. The proposed FE model can accurately predict the collapse pressure of faceted and conventional pipes. Results showed that the faceted pipe can boost the collapse capacity by at least an 80% increase compared to the conventional pipe. Also, the collapse mode was observed INTRODUCTION In today's world, subsea pipeline systems are construed as the most influential means to transport oil and gas. The rapid development that the oil and gas industry has witnessed necessitates the construction of thousands of kilometres of pipelines across the world. Given that these pipelines are lengthy, it is highly probable that they cross active faults (on land and in the sea); accordingly, they are in constant exposure to various catastrophic hazards. The characteristic distinguishing this kind of pipeline from other structures constructed on the ground is that the inertial forces exerted by the pipe's weight and its content are not very important. The most important structure damages occurring in pipelines are caused by collapse pressure if the external hydrostatic pressure of the pipeline is larger than its critical pressure. As a failure form, collapse will not only produce enormous economic loss but also result in large catastrophe to the ocean environment and ecosystem system (Drumond et al., 2018). Therefore, this phenomenon causes fracture in the pipe wall which is investigated by several researchers (Yeh and Kyriakides, 1986; Gong et al. 2013; He et al. 2014; Alrsai et al. 2018b) or leads to local buckling. A local buckle, ovalization, dent, or corrosion in the pipe wall can quickly transform the pipe cross-section into a dumb-bell shape that propagates along the pipeline as long as the external pressure is high enough to sustain propagation.
Collapse Mechanisms of Composite Pipelines Under External Pressure
Wei, Zichen (Griffith School of Engineering and Built Environment, Griffith University) | Karampour, Hassan (Griffith School of Engineering and Built Environment, Griffith University) | Guan, Hong (Griffith School of Engineering and Built Environment, Griffith University) | Rasheed, Hayder (Kansas State University) | Lin, Hong (College of Pipeline and Civil Engineering, China University of Petroleum (East China))
ABSTRACT This study investigates the effect of wrapping carbon fiber reinforced polymer (CFRP) over conventional steel offshore pipelines on improving their capacity under external hydrostatic pressure. Buckling performance of bare steel pipelines (conventional) and composite pipes (CFRP-strengthened) subjected to external pressure are examined analytically and numerically. In composite pipelines, the cylindrical steel tubes are wrapped with CFRP in 0/90° and ±45° fiber orientations. The finite element analysis (FEA) results are validated against analytical solutions on buckling of bare and composite pipelines. A parametric study is also carried out to investigate the effect of D/t ratio, the ratio of the thickness of the FRP to the steel-wall thickness, and the fiber orientation on the buckling capacity of composite pipelines. A good agreement between the current FEA and theoretical results are observed for pipelines with D/t > 30. Results also show that wrapping 0/90° cross-ply CFRP on the conventional steel pipes is more efficient in bucking resistance than the ±45° one. Using 0/90° orientation wrapping, the collapse pressure of a thin pipelines (D/t=100) can be enhanced by a factor of 15. INTRODUCTION Exploration of hydrocarbons has shifted to deep and ultra-deep waters due to the scarcity of near-shore resources and recent advancements in deep water drilling technologies. Pipelines are long tubular structures used to transport hydrocarbons over long distances, and are designed to resist installation, operation and environment loads safely during their design lives. During installation and shutdown, an empty pipeline undergoes large external pressure due to the hydrostatic load, which may cause collapse in the tube wall. In addition, high-pressure and high-temperature (HP/HT) pipelines may collapse under combined loading due to the interaction between external pressure and thermal loads (Karampour et al., 2015; Karampour, 2018) or seismic loads (Mina et al., 2020). Subsea pipelines are slender structures that can experience several structural instabilities. Global buckling can occur through lateral or upheaval buckling modes, however, these two buckling modes are not essentially failure modes (Karampour et al., 2013). Propagation buckling is the most critical one that increases the chance of pipeline failure, especially in the ultra-deep waters (Albermani et al., 2011; Karampour et al., 2017; Stephan et al., 2016; Alrsai et al., 2018a; Alrsai et al., 2018b). Hence, in deep waters, the failure mode associated with the buckle initiation and its propagation is the main consideration in the pipeline design.
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- Energy > Oil & Gas > Upstream (1.00)
- Government > Regional Government > North America Government > United States Government (0.46)
Local Buckling Failure Analysis of Deep Sea CFRP Armour Unbonded Flexible Riser
Shen, Yijun (State Key Laboratory of Marine Resources Utilization in South China Sea, Hainan University) | Liu, Hu (State Key Laboratory of Marine Resources Utilization in South China Sea, Hainan University / School of Civil and Architectural Engineering, Hainan University)
ABSTRACT As the oil and gas industry turns to the deep sea, flexible risers are becoming more and more widely used. To effectively achieve the lightweight and high strength requirements of ultra deep-water oil and gas development, it is a new trend to replace steel with CFRP. For deep-water flexible riser systems, the riser is bearing axial load, bending, and pressure during installation and operation, which may lead to local buckling. The carbon fiber reinforced material replaces the steel of tensile armor with a higher strength-to-weight ratio compared to metal risers, but its performance in deep water environments is less experienced. Firstly, this paper mainly describes the buckling behavior of a flexible riser, a 3D FE model was established by using ABAQUS to study the radial buckling mechanism. Then, to study the influence of different conditions on the buckling behavior through numerical simulation. Finally, the results of the finite element model are compared with the experimental data to provide some theoretical experience for the actual design and manufacture of CFRP in a flexible riser. INTRODUCTION Since the 21st century, resource development has gradually moved from land to sea. Flexible riser plays a key role in the development of deep-sea oil and gas resources. The traditional flexible riser is mainly made of the structure layer of metal materials and the functional layer of polymer materials. The structure layer is mainly made of high-strength steel such as carbon steel, stainless steel, etc. Nowadays, Resource development moves to the deep sea from the shallows gradually, and the weight of the flexible pipe has increased following the deepened of oil and gas exploitation, so comes with the broader size of the platform. Traditional steel is with deficiencies like short service life and complicated maintenance in the face of high-temperature corrosion of oil and gas. To solve these problems, people turn to fiber reinforced materials, such as Aramid, Glass, and Carbon fiber, to replace the steel in the structural layer of flexible riser. Fiber reinforced materials show further elevated specific strength low density, excellent fatigue resistance, and corrosion resistance, and thus replacing traditional steel with carbon fiber is one of the solutions to solve the excessive weight and corrosion of flexible risers. During installation and operation, the riser may be subjected to axial compression and bending loads, as well as two potential mechanisms for stable failure of the pipe tensile armor: - Radial buckling, also known as Birdcaging, which is usually occurred under axial compressive load. - Lateral buckling, which is generally formed under cyclic bending load.
Abstract Collapse performance of a casing string subjected to external hydraulic pressure is one of the most important parameters in the deep water well casing design. It often becomes one of the governing factors in a casing design program. This paper investigates the quantitative effect of inherent circumferential residual stress (RS) on casing collapse resistane to external pressure through parametric Finite Element Analysis (FEA). Nonlinear elastic-plastic FEA study on casing collapse calculations have been performed. Different magnitudes and orientations of the initial circumferential residual stress were considered. Modified Riks method was used to predict the casing onsite collapse pressure as well as the post-collapse response. Parameters considered in the analysis include: (i) two material grades (L80 and Grade 135); (ii) for each material grade, ratio of outside diameter to wall thickness (i.e. D/t) ranging from 10 to 50; (iii) for each D/t ratio, initial circumferential residual stress at casing inner diameter (ID) ranging from -40% to +50% of the material yield strength (YS). Analysis results indicate that there is a highly nonlinear, parabolic-like dependence of collapse strength on the initial circumferential residual stress. Comparison of the FEA results to the predictions by Klever-Tamano Ultimate Limit-State (KT ULS) equation indicates that the KT ULS equation in the current API Technical Report 5C3 (API TR 5C3) does not capture this nonlinear relationship. This is probably due to the limitation of the API historical collapse test data upon which the KT ULS equation was calibrated to. The majority of the API historical collapse tests had the compressive residual stress at the casing ID. Moreover, the relationship between casing collapse strength and residual stress may be used as a guideline for potentially developing new high collapse casing by full-length residual stress control in mill production.
Abstract Flexible pipes and their accessories are a pillar in the ultra-deep water oil and gas exploration, making them the focal points of analyses for integrity management, risk reduction and performance of the entire system. Responsible for the connection between two flexible pipes or between pipes and equipment, the end fittings are considered, in certain applications, a critical point of the system, requiring special attention to its design in order to ensure the highest reliability and minimize its impacts on flexible pipe design. Every end fitting must, in its interface with the flexible pipe, provide internal and external sealing capacity as well as tensile strength when under various operational conditions. Additionally, the end fitting design should aim to reduce as much as possible the impact on the performance of the flexible pipe. The qualification tests are divided into 3 levels – small, mid, and full-scale – representing, respectively, the characterization of interfaces and materials, individual systems and the product as a whole. In addition to this division, the tests are also divided based on their load cases as static, such as burst, axial tension, external and internal pressure, and dynamic, such as cyclic tensile tests combined with internal pressure. All test results are related with predictions of design methodologies and application scenarios, thus validating the respective methodologies and categorizing the end fitting for an operational envelope. This article details a qualification program of a new model of end fitting for offshore flexible pipes evidencing the strategy adopted and applicability in shallow to ultra-deep water fields, under static or dynamic loads.
Abstract Recent papers introduced a triaxial leak criterion with hydrostatic dependence through the Mean Normal Stress P defined as the average of the three normal stresses. The new criterion with linear dependence on P required two leak constants. Example applications in these papers addressed American Petroleum Institute (API) connections. This paper applies the triaxial criterion to a generic premium connection and determines the leak constants from finite element analysis (FEA) for combined loads with tension. Instead of a linear dependence on P, the FEA results for the generic premium connection correlate better with a quadratic relationship in terms of (P - σn) where σn is the Lubinski neutral stress. The quantity (P - σn) is proportional to effective stress. Quadratic dependence means that three leak constants are needed for premium connections. A plot of the leak limit curve superimposed on the pipe-body yield envelope shows load combinations where leak occurs before the pipe yields. A key conclusion is that internal leak cannot occur without tension for the loads investigated. Indeed, with sufficient tension, both internal and external leak can occur at low pressures for this modified generic premium connection. Actual premium connections should be designed so this triaxial limit curve for leak is outside (or mostly outside) the pipe-body failure envelope.
Market demand pushes subsea developments into ultra-deep water. Pipelines installed in such environments require very thick walls to cope with the extreme hydrostatic pressure. However, the design criteria for local buckling under combined loading in one of the prevailing submarine-pipeline design standards, DNVGL-ST-F101 (2017), are stated to be valid only for pipelines with a diameter-to-wall-thickness ratio (D/t) between 15 and 45. The European Pipeline Research Group evaluated whether the existing design equations can be used for very thick-walled pipelines with D/t below 15 that are subject to external pressure and bending, without affecting the level of conservatism underlying the code framework. Based on the adopted assumptions, the limit-state formulation for load-controlled behaviour was found to be increasingly conservative if D/t reduces and the pressure is relatively close to the collapse pressure. Introduction Intecsea reviewed the status of deep-water pipeline technology for the European Pipeline Research Group (EPRG) Design Committee as part of EPRG Project 178/2015 (“Deep water pipelines – Gap analysis”). This study covers a gap analysis and was concluded in 2016. Areas that require further research were identified and subsequently included in EPRG’s research road map. An important gap is the absence of a reliable and valid limit-state formulation for local buckling of thick-walled pipe when loaded by a combination of bending, axial force, and pressure. The limit-state formulations for local buckling included in DNVGL-ST-F101 (DNV GL, 2017), which is widely used for the design of subsea pipelines, are stated not to be valid when the diameter-to-wall-thickness ratio (D/t) is less than 15.
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