The Experts below are selected from a list of 159 Experts worldwide ranked by ideXlab platform
Olav Aamlid - One of the best experts on this subject based on the ideXlab platform.
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Effective Axial Force in multi-layered cylinders with applications to insulated offshore pipelines
Engineering Structures, 2018Co-Authors: Knut Vedeld, Olav Fyrileiv, Leif Collberg, Håvar A. Sollund, Olav AamlidAbstract:Abstract To ensure high content temperature, some offshore pipelines have insulation coating made from polypropylene or polyethylene. Typical coating systems have significantly lower stiffness than ordinary carbon manganese steel, but also significantly higher temperature expansion coefficients. Due to the differences in material properties, insulation coating systems have a non-trivial influence on the critical design parameter called the Effective Axial Force in offshore pipelines. Current offshore design codes do not contain guidance on how to include the effects of coating systems on the Effective Axial Force. In this paper, an exact analytical formula for the Effective Axial Force in pipelines with arbitrarily many layers is deduced, accounting also for temperature variation along the radial coordinate. A simplified approximate formula, which is more suitable for use in engineering contexts, is developed and its validity verified by comparisons to results of the exact one.
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Advanced Lateral Stability Analyses for Lightweight Pipelines on Clay: A Case Study
29th International Conference on Ocean Offshore and Arctic Engineering: Volume 5 Parts A and B, 2010Co-Authors: Ha˚var Sollund, Knut Vedeld, Olav AamlidAbstract:In 2007 DNV issued the new recommended practice DNV-RP-F109 On-Bottom Stability Design of Submarine Pipelines which replaced RP-E305 from 1988 with the same title. The new DNV-RP-F109 describes three different design approaches; full dynamic analysis, absolute static stability, and the generalized method with design curves for virtually stable pipes (allowing up to 0.5 diameters lateral displacement) and for up to 10 pipe diameters displacement in an extreme storm condition. DNV-RP-F109 recommends limiting the sum of the lateral displacement in the temporary condition and during operation to 10 diameters. For larger displacements one should perform a full dynamic analysis and special considerations with respect to bending and fatigue should be made. This paper is concerned with the consequences of exceeding the 10-diameter displacement criterion described in DNV-RP-F109, and how to use different methodologies in accordance with DNV-RP-F109 to ensure limited lateral displacements, acceptable environmental loads/strains and limited/acceptable fatigue damage accumulation. The methodologies covered in this paper include advanced assessments of passive resistance in soil, and account for increased vertical penetration due to laying and lateral fixation of the pipe at regular intervals. For the laterally restricted pipe, studies on reaction Forces and reaction moments are made in addition to fatigue estimations at the points of maximum local longitudinal stress. Variations in environmental conditions, soil conditions and levels of Effective Axial Force have also been considered.Copyright © 2010 by ASME
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Effects of Free Spans on Lateral Stability of Offshore Pipelines: A Local Approach
29th International Conference on Ocean Offshore and Arctic Engineering: Volume 5 Parts A and B, 2010Co-Authors: Knut Vedeld, Ha˚var Sollund, Olav AamlidAbstract:Current industry practice on determination of necessary weight for lateral stability of offshore pipelines makes many important assumptions on the boundary conditions and initial configurations of a subsea pipeline. The pipe is assumed to be on a flat seabed, the distance between local constraints of the pipeline is assumed to be so large that the boundary conditions at the ends have no influence on the maximum lateral displacement, and the contact between seabed and pipeline is assumed to be uniform. Pipelines are in reality placed on rough seabed, and the contact between pipeline and seabed may be very non-uniform. Therefore it is necessary to investigate the effects of free spans and their influence on lateral stability. Pipelines in free spans experience much lower hydrodynamic loads, including lift, drag and inertia, but at the same time a reduced overall resistance. The local influence of the free span is governed by span gap, span length, soil properties, pipe geometry, Effective Axial Force and pipe submerged weight. Local studies of lateral stability on span shoulders have been performed using a simplified approach according to the absolute stability criterion and penetration models according to DNV-RP-F109, and the influence with respect to design according to the absolute static stability criterion is shown. It is demonstrated in this paper that local displacements on free span shoulders may occur even if the pipe satisfies the absolute stability criterion. However, the overall effects of free spans [2] are fairly minor on the global pipeline behaviour, even for pipes with a high ratio of spans to contact points. Therefore, the displacements demonstrated in this paper are likely to be local to smaller areas on span shoulders.© 2010 ASME
Knut Vedeld - One of the best experts on this subject based on the ideXlab platform.
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Effective Axial Force in multi-layered cylinders with applications to insulated offshore pipelines
Engineering Structures, 2018Co-Authors: Knut Vedeld, Olav Fyrileiv, Leif Collberg, Håvar A. Sollund, Olav AamlidAbstract:Abstract To ensure high content temperature, some offshore pipelines have insulation coating made from polypropylene or polyethylene. Typical coating systems have significantly lower stiffness than ordinary carbon manganese steel, but also significantly higher temperature expansion coefficients. Due to the differences in material properties, insulation coating systems have a non-trivial influence on the critical design parameter called the Effective Axial Force in offshore pipelines. Current offshore design codes do not contain guidance on how to include the effects of coating systems on the Effective Axial Force. In this paper, an exact analytical formula for the Effective Axial Force in pipelines with arbitrarily many layers is deduced, accounting also for temperature variation along the radial coordinate. A simplified approximate formula, which is more suitable for use in engineering contexts, is developed and its validity verified by comparisons to results of the exact one.
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Effective Axial Forces in offshore lined and clad pipes
Engineering Structures, 2014Co-Authors: Knut Vedeld, Håvar A. Sollund, Jostein Hellesland, Olav FyrileivAbstract:To protect pipelines from corrosion attacks, some offshore pipelines have corrosion resistant liners or cladding made from stainless steel. Stainless steels have higher temperature expansion coefficients and lower Poisson’s ratios than ordinary high strength carbon manganese steels. Due to the differences in material properties, liners and cladding have a non-trivial influence on the critical design parameter called the Effective Axial Force in offshore pipelines. Current offshore design codes do not contain guidance on how to include the effects of liners and cladding on the Effective Axial Force. In this paper, an exact analytical formula for the Effective Axial Force in lined and clad pipes is deduced. A simplified approximate formula, which is more suitable for use in engineering contexts, is developed and its validity verified by comparisons to results of the complex exact one.
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A finite element solver for modal analysis of multi-span offshore pipelines
2014Co-Authors: Håvar A. Sollund, Knut VedeldAbstract:Accurate determination of pipeline eigenfrequencies and mode shapes is essential to free span design. For pipelines resting on rough seabeds, multiple free spans are commonly located sufficiently close to be interacting, and finite element analysis (FEA) is then conventionally required to determine the modal response. In the present report, a tailor-made (specific purpose) FEA tool is developed to carry out modal analyses of multi-span offshore pipelines. The specific purpose FEA tool is thoroughly validated by comparisons to analytical results and to results obtained using the general purpose FEA software Abaqus. Several beam and pipeline configurations are studied, ranging from simplified analyses of simply supported beams to sophisticated analyses of challenging multi-span pipeline sections, using actual seabed survey data. The validation study therefore gives valuable insight into the dynamic response of multi-span subsea pipelines. Compared to general purpose FEA modeling, the specifically designed FEA tool offers more flexible adjustment of element resolution in critical areas, more efficient file storage utilization, and also allows the designer to improve aspects of the physical modeling. The latter includes the possibility of using a consistent soil stiffness formulation rather than a traditional lumped soil model with discrete springs, as well as applying different added mass coefficients in Axial and transverse directions. The impact on the modal response quantities of adopting a consistent soil stiffness model and directional variation in added mass is investigated. In addition, a methodology for establishing the static configuration and the Effective Axial Force distribution along the pipeline using the general purpose FEA software Abaqus is described.
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Advanced Lateral Stability Analyses for Lightweight Pipelines on Clay: A Case Study
29th International Conference on Ocean Offshore and Arctic Engineering: Volume 5 Parts A and B, 2010Co-Authors: Ha˚var Sollund, Knut Vedeld, Olav AamlidAbstract:In 2007 DNV issued the new recommended practice DNV-RP-F109 On-Bottom Stability Design of Submarine Pipelines which replaced RP-E305 from 1988 with the same title. The new DNV-RP-F109 describes three different design approaches; full dynamic analysis, absolute static stability, and the generalized method with design curves for virtually stable pipes (allowing up to 0.5 diameters lateral displacement) and for up to 10 pipe diameters displacement in an extreme storm condition. DNV-RP-F109 recommends limiting the sum of the lateral displacement in the temporary condition and during operation to 10 diameters. For larger displacements one should perform a full dynamic analysis and special considerations with respect to bending and fatigue should be made. This paper is concerned with the consequences of exceeding the 10-diameter displacement criterion described in DNV-RP-F109, and how to use different methodologies in accordance with DNV-RP-F109 to ensure limited lateral displacements, acceptable environmental loads/strains and limited/acceptable fatigue damage accumulation. The methodologies covered in this paper include advanced assessments of passive resistance in soil, and account for increased vertical penetration due to laying and lateral fixation of the pipe at regular intervals. For the laterally restricted pipe, studies on reaction Forces and reaction moments are made in addition to fatigue estimations at the points of maximum local longitudinal stress. Variations in environmental conditions, soil conditions and levels of Effective Axial Force have also been considered.Copyright © 2010 by ASME
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Effects of Free Spans on Lateral Stability of Offshore Pipelines: A Local Approach
29th International Conference on Ocean Offshore and Arctic Engineering: Volume 5 Parts A and B, 2010Co-Authors: Knut Vedeld, Ha˚var Sollund, Olav AamlidAbstract:Current industry practice on determination of necessary weight for lateral stability of offshore pipelines makes many important assumptions on the boundary conditions and initial configurations of a subsea pipeline. The pipe is assumed to be on a flat seabed, the distance between local constraints of the pipeline is assumed to be so large that the boundary conditions at the ends have no influence on the maximum lateral displacement, and the contact between seabed and pipeline is assumed to be uniform. Pipelines are in reality placed on rough seabed, and the contact between pipeline and seabed may be very non-uniform. Therefore it is necessary to investigate the effects of free spans and their influence on lateral stability. Pipelines in free spans experience much lower hydrodynamic loads, including lift, drag and inertia, but at the same time a reduced overall resistance. The local influence of the free span is governed by span gap, span length, soil properties, pipe geometry, Effective Axial Force and pipe submerged weight. Local studies of lateral stability on span shoulders have been performed using a simplified approach according to the absolute stability criterion and penetration models according to DNV-RP-F109, and the influence with respect to design according to the absolute static stability criterion is shown. It is demonstrated in this paper that local displacements on free span shoulders may occur even if the pipe satisfies the absolute stability criterion. However, the overall effects of free spans [2] are fairly minor on the global pipeline behaviour, even for pipes with a high ratio of spans to contact points. Therefore, the displacements demonstrated in this paper are likely to be local to smaller areas on span shoulders.© 2010 ASME
Ha˚var Sollund - One of the best experts on this subject based on the ideXlab platform.
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Advanced Lateral Stability Analyses for Lightweight Pipelines on Clay: A Case Study
29th International Conference on Ocean Offshore and Arctic Engineering: Volume 5 Parts A and B, 2010Co-Authors: Ha˚var Sollund, Knut Vedeld, Olav AamlidAbstract:In 2007 DNV issued the new recommended practice DNV-RP-F109 On-Bottom Stability Design of Submarine Pipelines which replaced RP-E305 from 1988 with the same title. The new DNV-RP-F109 describes three different design approaches; full dynamic analysis, absolute static stability, and the generalized method with design curves for virtually stable pipes (allowing up to 0.5 diameters lateral displacement) and for up to 10 pipe diameters displacement in an extreme storm condition. DNV-RP-F109 recommends limiting the sum of the lateral displacement in the temporary condition and during operation to 10 diameters. For larger displacements one should perform a full dynamic analysis and special considerations with respect to bending and fatigue should be made. This paper is concerned with the consequences of exceeding the 10-diameter displacement criterion described in DNV-RP-F109, and how to use different methodologies in accordance with DNV-RP-F109 to ensure limited lateral displacements, acceptable environmental loads/strains and limited/acceptable fatigue damage accumulation. The methodologies covered in this paper include advanced assessments of passive resistance in soil, and account for increased vertical penetration due to laying and lateral fixation of the pipe at regular intervals. For the laterally restricted pipe, studies on reaction Forces and reaction moments are made in addition to fatigue estimations at the points of maximum local longitudinal stress. Variations in environmental conditions, soil conditions and levels of Effective Axial Force have also been considered.Copyright © 2010 by ASME
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Effects of Free Spans on Lateral Stability of Offshore Pipelines: A Local Approach
29th International Conference on Ocean Offshore and Arctic Engineering: Volume 5 Parts A and B, 2010Co-Authors: Knut Vedeld, Ha˚var Sollund, Olav AamlidAbstract:Current industry practice on determination of necessary weight for lateral stability of offshore pipelines makes many important assumptions on the boundary conditions and initial configurations of a subsea pipeline. The pipe is assumed to be on a flat seabed, the distance between local constraints of the pipeline is assumed to be so large that the boundary conditions at the ends have no influence on the maximum lateral displacement, and the contact between seabed and pipeline is assumed to be uniform. Pipelines are in reality placed on rough seabed, and the contact between pipeline and seabed may be very non-uniform. Therefore it is necessary to investigate the effects of free spans and their influence on lateral stability. Pipelines in free spans experience much lower hydrodynamic loads, including lift, drag and inertia, but at the same time a reduced overall resistance. The local influence of the free span is governed by span gap, span length, soil properties, pipe geometry, Effective Axial Force and pipe submerged weight. Local studies of lateral stability on span shoulders have been performed using a simplified approach according to the absolute stability criterion and penetration models according to DNV-RP-F109, and the influence with respect to design according to the absolute static stability criterion is shown. It is demonstrated in this paper that local displacements on free span shoulders may occur even if the pipe satisfies the absolute stability criterion. However, the overall effects of free spans [2] are fairly minor on the global pipeline behaviour, even for pipes with a high ratio of spans to contact points. Therefore, the displacements demonstrated in this paper are likely to be local to smaller areas on span shoulders.© 2010 ASME
Colin Cross - One of the best experts on this subject based on the ideXlab platform.
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A NEW HOLISTIC APPROACH FOR SUBSEA PIPELINE UPHEAVAL BUCKLING DESIGN
Journal of Offshore Mechanics and Arctic Engineering, 2017Co-Authors: M. Liu, Colin CrossAbstract:For a trenched and buried pipeline, the propensity to upheaval buckling (UHB) is a major design concern. Predictive UHB design is typically required at the outset to determine both trenching and backfilling requirements. Additional rockdump schedule can be established by analyzing post pipelay out of straightness (OOS) survey data incorporating appropriate safety factors based on a structural reliability analysis (SRA). The normal approach is to examine the as-laid pipeline imperfection survey statistics and data accuracy. The structural reliability analysis and load factor calculation are typically performed a priori based on the assumed initial imperfections using the universal design curve methodology. A new pseudo-energy method for UHB and OOS is proposed and discussed in this paper based on the variational principle and modal analysis. The approach takes into account the effects of varying Effective Axial Force, trench imperfections, and vertical uplift resistance, by combining both Axial friction and lateral resistance methods into a unified model. A new concept, Effective uplift resistance and associated load, is also introduced to deal with nonuniform backfill cover. Adjacent imperfections and backfill profiles are considered in detail. A finite element (FE) model is developed to consist of three-noded quadratic pipe elements using abaqus Ver 6.12, and iterations of FE analyses are performed to demonstrate the tangible benefits of the approach specifically for UHB OOS design in relation to target trenching and backfilling, leading to improved reliability and potential cost saving in UHB OOS design and rockdump installation.
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Subsea Pipeline UHB Design: An Improved Analysis Approach
Volume 5: Pipelines Risers and Subsea Systems, 2016Co-Authors: M. Liu, Colin CrossAbstract:A subsea pipeline operating at temperature and pressure may buckle both vertically and laterally. For a trenched and buried pipeline, the propensity to upheaval buckling (UHB) is a major design concern. Predictive UHB design is typically required at the outset to determine both trenching and backfilling requirements. Additional rockdump schedule can be established by analysing post pipelay OOS survey data incorporating appropriate safety factors based on a structural reliability analysis. The normal approach is to examine the pipeline imperfection survey statistics and data accuracy. The structural reliability analysis and load factor calculation is typically performed a priori based on the assumed imperfections using the methodology outlined in ref [1]. The additional rockdump schedule is derived from the crown of the pipeline imperfections regardless of adjacent profiles and overall backfill data. A new pseudo energy method for UHB and OOS is proposed and discussed in this paper based on the variational principle and modal analysis. The approach takes into account the effects of varying Effective Axial Force, trench imperfections and vertical uplift resistance, by combining both Axial friction and lateral resistance methods into a unified model. A new concept, Effective uplift resistance and associated load is also introduced to deal with non-uniform backfill cover. Adjacent imperfections and backfill profiles are considered in detail. An FE model is developed to consist of 3-noded quadratic pipe elements using ABAQUS Ver 6.12 and iterations of FE analyses are performed to demonstrate the tangible benefits of the approach specifically for UHB OOS design in relation to target trenching and backfilling, leading to improved reliability and potential cost saving in UHB OOS design and rockdump installation.
Nelson Szilard Galgoul - One of the best experts on this subject based on the ideXlab platform.
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The Influence of Internal Pressure on Pipeline Natural Frequency
Volume 3: Pipeline and Riser Technology, 2009Co-Authors: Andre´ Luiz Lupinacci Massa, Nelson Szilard Galgoul, Nestor Oscar Guevara Junior, Antonio Carlos Fernandes, Fabio M. Coelho, Severino Fonseca Da Silva NetoAbstract:Galgoul et al. (2004) have written a previous paper in which they have pointed out the conservatism of the latest recommendations for pipeline freespan evaluations, associated to the way the Axial Force is considered in the determination of the pipeline natural frequency. First because it fails to consider the fact, that the Axial Force of a sagging pipe, subject to temperature expansion, is much smaller than that of a straight pipe. Second because the Effective Axial Force caused by internal pressure should not be used to determine the pipeline natural frequency. Fyrileiv and Collberg (2005) also discussed this aspect. In order to back up their previous arguments the authors decided to perform some tests an Axially restrained pipeline at both ends, which was pressurized in order to justify their claims that these pipelines are not only under tension (and not compression), but also that their natural frequencies increase instead of reducing, although they do bend out because of the pressure, reaching a point of instability. The authors understand the Effective Axial Force concept and the enormous simplifications, which it brings to an otherwise cumbersome problem, but wish to emphasize that these advantages are not unlimited and that this is one of these restrictions. To back up the text results a finite element model has been produced, in which the internal pressure is taken into account as it actually is (and not as an Axial Force) to show that the pipe wall stresses can only be obtained correctly in this manner.
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A Discussion on How Internal Pressure is Treated in Offshore Pipeline Design
2004 International Pipeline Conference Volumes 1 2 and 3, 2004Co-Authors: Nelson Szilard Galgoul, Andre´ Luiz Lupinacci Massa, Cla´udia Albergaria ClaroAbstract:The design of rigid submarine pipelines has been the object of extensive research work over the last few years, where the most relevant issues include upheaval and lateral buckling problems. Both of these problems systematically associate temperature and pressure loads, where the treatment of the first is obvious, while the latter have always been a matter of discussion. In 1974 Palmer and Baldry [1] presented a theoretical-experimental contribution, in which they have set a pattern that has been followed ever since. Another similar and well known paper was published by Sparks in 1983 [7], who only present a physical interpretation of this same theory. Most of the present day industry codes define an Effective Axial Force, according to which, fixed end pipelines will be under compression due to internal pressure. The starting point of the discussion presented in [1] was that internal pressure produces a lateral Force, which is numerically equal to the pressure times internal cross-sectional area times the pipeline curvature: q = p.Ai.d2y/dx2 (1) This equation is demonstrated further ahead in this paper. Palmer and Baldry then based their arguments on the traditional equation of the pinned column buckling problem, studied by Euler [2]: EId4y/dx4 + Pd2y/dx2 = 0 (2) for which the well known solution is: P = π2EI/L2 (3) and on the associated problem studied by Timoshenko [3], which adds a distributed lateral load q to the same problem: EId4y/dx4 + Pd2y/dx2 = q (4) Replacing q with the lateral pressure given above, they were able to have their own problem fall back onto the Euler solution: EId4y/dx4 + Pd2y/dx2 = p.Ai.d2y/dx2P-pAi = π2EI/L2 (5) After correcting for the Poisson effect they were able to determine the new critical Axial Force caused by the pressure. Unfortunately, however, the arguments set forth in [1] have been misunderstood. The fact that both Axial Force and lateral Force multiply curvature does not make them Forces of the same nature. Being able to add them has solved a mathematical equation, but still hasn’t converted the lateral Force to Axial. The authors wish to prove that [1] presents no more than a tool, which can be used in the analysis of global buckling problems of pipelines subject to both temperature and pressure. It will be shown, however, that this pressure will not produce an Axial Force, as now-a-days prescribed conservatively in many pipeline codes, which is even used for stress checking.Copyright © 2004 by ASME