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- Herausgeber: John Wiley & Sons
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
The technology, processes, materials, and theories surrounding pipeline construction, application, and troubleshooting are constantly changing, and this new series, Advances in Pipes and Pipelines, has been created to meet the needs of engineers and scientists to keep them up to date and informed of all of these advances. This second volume in the series focuses on flexible pipelines, risers, and umbilicals, offering the engineer the most thorough coverage of the state-of-the-art available. The authors of this work have written numerous books and papers on these subjects and are some of the most influential authors on flexible pipes in the world, contributing much of the literature on this subject to the industry. This new volume is a presentation of some of the most cutting-edge technological advances in technical publishing. The first volume in this series, published by Wiley-Scrivener, is Flexible Pipes, available at www.wiley.com. Laying the foundation for the series, it is a groundbreaking work, written by some of the world's foremost authorities on pipes and pipelines. Continuing in this series, the editors have compiled the second volume, equally as groundbreaking, expanding the scope to pipelines, risers, and umbilicals. This is the most comprehensive and in-depth series on pipelines, covering not just the various materials and their aspects that make them different, but every process that goes into their installation, operation, and design. This is the future of pipelines, and it is an important breakthrough. A must-have for the veteran engineer and student alike, this volume is an important new advancement in the energy industry, a strong link in the chain of the world's energy production.
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Veröffentlichungsjahr: 2020
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Table of Contents
Cover
Title page
Copyright
Preface
Acknowledgment
About the Author
Part 1: LOCAL ANALYSIS
1 Introduction
1.1 Flexible Pipelines Overview
1.2 Environmental Conditions
1.3 Flexible Pipeline Geometry
1.4 Base Case-Failure Modes and Design Criteria
1.5 Reinforcements
1.6 Project and Objectives
References
2 Structural Design of Flexible Pipes in Different Water Depth
2.1 Introduction
2.2 Theoretical Models
2.3 Comparison and Discussion
2.4 Conclusions
References
3 Structural Design of High Pressure Flexible Pipes of Different Internal Diameter
3.1 Introduction References
3.2 Analytical Models
3.3 FEA Modeling Description
3.4 Result and Discussion
3.5 Design
3.6 Conclusions
References
4 Tensile Behavior of Flexible Pipes
4.1 Introduction
4.2 Theoretical Models
4.3 Numerical Model
4.4 Comparison and Discussion
4.5 Parametric Study
4.6 Conclusions
References
5 Design Case Study for Deep Water Risers
5.1 Abstract
5.2 Introduction
5.3 Cross-Sectional Design
5.4 Case Study
5.5 Design Result
5.6 Finite Elements Analysis
5.7 Conclusion
References
6 Unbonded Flexible Pipe Under Bending
6.1 Introduction
6.2 Helical Layer Within No-Slip Range
6.3 Helical Layer Within Slip Range
References
7 Coiling of Flexible Pipes
7.1 Introduction
7.2 Local Analysis
7.3 Global Analysis
7.4 Parametric Study
7.5 Conclusions
References
Part 2: RISER ENGINEERING
8 Flexible Risers and Flowlines
8.1 Introduction
8.2 Flexible Pipe Cross-Section
8.3 End Fitting and Annulus Venting Design
8.4 Flexible Riser Design
References
9 Lazy-Wave Static Analysis
9.1 Introduction
9.2 Fundamental Assumptions
9.3 Configuration Calculation
9.4 Numerical Solution
9.5 Finite Element Model
9.6 Comparison and Discussion
9.7 Parameter Analysis
9.8 Conclusions
References
10 Steep-Wave Static Configuration
10.1 Introduction
10.2 Configuration Calculation
10.3 Numerical Solution
10.4 Comparison and Discussion
10.5 Parametric Analysis
10.6 Conclusions
References
11 3D Rod Theory for Static and Dynamic Analysis
11.1 Introduction
11.2 Nomenclature
11.3 Mathematical Model
11.4 Case Study
11.5 Results and Discussion
11.6 Conclusions
References
12 Dynamic Analysis of the Cable-Body of the Deep Underwater Towed System
12.1 Introduction
12.2 Establishment of Towed System Dynamic Model
12.3 Numerical Simulation and Analysis of Calculation Results
12.4 Conclusions
Acknowledgments
References
13 Dynamic Analysis of Umbilical Cable Under Interference
13.1 Introduction
13.2 Dynamic Model of Umbilical Cable
13.3 The Establishment of Dynamic Simulation Model in OrcaFlex
13.4 The Calculation Results
13.5 Conclusion
References
14 Fatigue Analysis of Flexible Riser
14.1 Introduction
14.2 Fatigue Failure Mode of Flexible Riser
14.3 Global Model of Flexible Risers
14.4 Failure Mode and Design Criteria
14.5 Calculation Method of Fatigue Life of Flexible Riser
14.6 Example of Fatigue Life Analysis of Flexible Riser
References
15 Steel Tube Umbilical and Control Systems
15.1 Introduction
15.2 Control Systems
15.3 Cross-Sectional Design of the Umbilical
15.4 Steel Tube Design Capacity Verification
15.5 Extreme Wave Analysis
15.6 Manufacturing Fatigue Analysis
15.7 In-Place Fatigue Analysis
15.8 Installation Analysis
15.9 Required On-Seabed Length for Stability
References
16 Stress and Fatigue of Umbilicals
16.1 Introduction
16.2 STU Fatigue Models
16.3 Worked Example
16.4 Conclusions
16.5 Recommendations
References
17 Cross-Sectional Stiffness for Umbilicals
17.1 Introduction
17.2 Theoretical Model of Umbilicals
17.3 Bending Stiffness of Umbilicals
17.4 Tensile Stiffness of Umbilicals
17.5 Torsional Stiffness of Umbilicals
17.6 Ultimate Capacity of Umbilicals
References
18 Umbilical Cross-Section Design
18.1 Introduction
18.2 Umbilicals Cross-Section Design Overview
18.3 Umbilical Cable Cross-Section Design
References
Part 3: FIBER GLASS REINFORCED DEEP WATER RISERS
19 Collapse Strength of Fiber Glass Reinforced Riser
19.1 Introduction
19.2 External Pressure Test
19.3 Theoretical Analysis
19.4 Numerical Analysis
19.5 Finite Element Analysis
19.6 Conclusion
References
20 Burst Strength of Fiber Glass Reinforced Riser
20.1 Introduction
20.2 Experiment
20.3 Numerical Simulations
20.4 Analytical Solution
20.5 Results and Discussion
20.6 Parametric Analysis
20.7 Conclusions
References
21 Structural Analysis of Fiberglass Reinforced Bonded Flexible Pipe Subjected to Tension
21.1 Introduction
21.2 Experiment
21.3 Theoretical Solution
21.4 Finite Element Model
21.5 Comparison and Discussion
21.6 Parametric Study
21.7 Conclusions
Acknowledgement
References
22 Fiberglass Reinforced Flexible Pipes Under Bending
22.1 Introduction
22.2 Experiment
22.3 Analytical Solution
22.4 Finite Element Method
22.5 Result and Conclusion
22.6 Parametric Analysis
22.7 Conclusions
References
23 Fiberglass Reinforced Flexible Pipes Under Torsion
23.1 Introduction
23.2 Experiments
23.3 Experimental Results
23.4 Analytical Solution (
k
= 2, 3 … (
n
− 1)) (k = 1, n)
23.5 Numerical Simulations
23.6 Results and Discussions
23.7 Parametric Analysis
23.8 Conclusions
Acknowledgments
References
24 Cross-Section Design of Fiberglass Reinforced Riser
24.1 Introduction
24.2 Nomenclature
24.3 Basic Structure of Pipe
24.4 Strength Failure Design Criteria
24.5 Failure Criteria for Instability Design
24.6 Design Criteria for Leakage Failure
References
25 Fatigue Life Assessment of Fiberglass Reinforced Flexible Pipes
25.1 Introduction
25.2 Global Analysis
25.3 Rain Flow Method
25.4 Local Analysis
25.5 Modeling
25.6 Result Discussion
25.7 Sensitivity Analysis
25.8 Fatigue Life Assessment
25.9 Conclusion
References
Part 4: ANCILLARY EQUIPMENTS FOR FLEXIBLES AND UMBILICALS
26 Typical Connector Design for Risers
26.1 Introduction
26.2 Carcass
26.3 Typical Connector
26.4 Seal System
26.5 Termination of the Carcass
26.6 Smooth Bore Pipe
26.7 Rough Bore Pipe
26.8 Discussion
26.9 Conclusions
References
27 Bend Stiffener and Restrictor Design
27.1 Introduction
27.2 Response Model
27.3 Extreme Load Description
27.4 General Optimization Scheme
27.5 Application Example
27.6 Non-Dimensional Bend Stiffener Design
27.7 Alternative Non-Dimensional Parameters
27.8 Conclusions
References
28 End Termination Design for Umbilicals
28.1 Introduction
28.2 Umbilical Termination Assembly
28.3 Subsea Termination Interface
References
29 Mechanical Properties of Glass Fibre Reinforced Pipeline During the Laying Process
29.1 Introduction
29.2 Theoretical Analysis
29.3 Static Analysis
29.4 Dynamic Characteristic Analysis
29.5 Conclusions
References
Index
Also of Interest
End User License Agreement
List of Illustrations
Chapter 1
Figure 1.1 Employment of flexible pipelines as risers.
Figure 1.2 Unbonded composite-based flexible pipe.
Figure 1.3 Unbonded metal-based flexible pipe.
Figure 1.4 Interlocked carcass.
Figure 1.5 Pressure armor cross-section profiles.
Chapter 2
Figure 2.1 Schematic representation reference systems, initial radial displaceme...
Figure 2.2 Carcass profile-principal outline.
Figure 2.3 Parameterized carcass profile.
Figure 2.4 Full carcass cross section imported.
Figure 2.5 Carcass model geometry.
Figure 2.6 Steel strain-stress relationship.
Figure 2.7 Load and boundary conditions.
Figure 2.8 ALLKE/ALLSE versus dimensionless load.
Figure 2.9 Carcass model mesh details, cross-section, and surfaces.
Figure 2.10 U1 displacements.
Figure 2.11 U2 displacements.
Figure 2.12 Ovality versus dimensionless load.
Figure 2.13 Ovality versus load for different geometries, where dashed lines sta...
Figure 2.14 Critical loads versus dimensionless diameters.
Figure 2.15 Error trend.
Figure 2.16 Critical load comparison for all the model established versus dimens...
Figure 2.17 Results comparison for FEM and modified theoretical model.
Figure 2.18 Stress-strain relationship.
Figure 2.19 HDPE stress-strain relationship.
Chapter 3
Figure 3.1 Structure of flexible pipe.
Figure 3.2 Cylindrical mathematical parameters definition.
Figure 3.3 Helix mathematical parameters definition.
Figure 3.4 Pressure armor cross section profile.
Figure 3.5 Kinematic Coupling at RP-2.
Figure 3.6 Meshing of the flexible pipe model.
Figure 3.7 Kinetic energy/internal energy curve.
Figure 3.8 Artificial strain energy/strain energy curve.
Figure 3.9 Model of pressure armor layer.
Figure 3.10 Mises stress of Z-shaped section.
Figure 3.11 Pressure-maximum von Mises stress curve.
Figure 3.12 Pressure-axial displacement curve.
Figure 3.13 Pressure-radial displacement curve.
Figure 3.14 Computer design flowchart of pipe section.
Chapter 4
Figure 4.1 Linear-longitudinal profile.
Figure 4.2 Contact pressures between layers mechanical model of pressure armor l...
Figure 4.3 Pressure armor profile-principal outline.
Figure 4.4 Contact pressure and equivalent radii.
Figure 4.5 Contraction and elongation for a representative pitch length of tensi...
Figure 4.6 Radial loading condition of tensile armor layer.
Figure 4.7 Pressure armor-parameterized cross-section (lengths in millimeters an...
Figure 4.8 Pressure armor’s load and boundary conditions.
Figure 4.9 Pressure armor mesh.
Figure 4.10 Strain and kinetic energies against load.
Figure 4.11 Pressure against radial displacements for two representative points.
Figure 4.12 Steel stress-strain relationship.
Figure 4.13 HDPE stress-strain relationship.
Figure 4.14 Reference point at the end surfaces.
Figure 4.15 Interlayered structure mesh.
Figure 4.16 Strain and kinetic energies.
Figure 4.17 Tensile force comparison.
Figure 4.18 Mises stress of pressure armor from FEM.
Figure 4.19 Points selected on the pressure armor external surface for contact p...
Figure 4.20 Tensile force comparison.
Figure 4.21 Contact pressure between pressure armor and inner tensile armor laye...
Figure 4.22 Contact pressure between tensile armor layers.
Figure 4.23 Mises stress—outer layer of wires.
Figure 4.24 Strain and stress distribution for outer tensile armor layer.
Figure 4.25 Mises stress comparison for inner tensile armor layer.
Figure 4.26 Mises stress comparison for outer tensile armor layer.
Figure 4.27 Tensile strength comparison for the pipe subjected to pure tension a...
Figure 4.28 MSFP-based reinforced longitudinal profile.
Figure 4.29 Tensile force comparison.
Chapter 5
Figure 5.1 Typical carcass profile.
Figure 5.2 Typical pressure armor.
Figure 5.3 Flow chart of design procedure.
Figure 5.4 Mathematical parameters definition.
Figure 5.5 Catenary configuration for the tension design.
Figure 5.6 Detailed geometry of FE model.
Figure 5.7 Burst failure mode of flexible pipe.
Figure 5.8 Tension failure mode of flexible pipe.
Figure 5.9 Collapse failure moment.
Chapter 6
Figure 6.1 Reference systems for toroid surface.
Figure 6.2 Cross-section of helical layer.
Figure 6.3 Darboux frame.
Figure 6.4 Micro-section of helical wire.
Figure 6.5 The sliding mechanism model.
Figure 6.6 The axial displacement of beam.
Figure 6.7 The axial force of beam.
Figure 6.8 The axial force of helical wire.
Figure 6.9 The axial force of helical wire.
Chapter 7
Figure 7.1 Pipe coiled in the reel drum.
Figure 7.2 Buckling failure of MSFP.
Figure 7.3 Pipe mechanics analysis in reeling.
Figure 7.4 Crosssection of MSFP.
Figure 7.5 MSFP with partly outer sheath peeling off.
Figure 7.6 Stress-strain curves of HDPE.
Figure 7.7 Stress-strain curves of steel strip.
Figure 7.8 Tensile test of MSFP.
Figure 7.9 Tension-extension curves of two specimens.
Figure 7.10 Diagrammatic sketch of bending machine.
Figure 7.11 Moment-curvature curves of two specimens.
Figure 7.12 MFSP specimen before and after bending.
Figure 7.13 Fitting tension-extension curve.
Figure 7.14 Fitting bending-curvature curve.
Figure 7.15 The global model of reeling operation.
Figure 7.16 The local direction of the beam element.
Figure 7.17 Mesh condition of the global model.
Figure 7.18 Load and boundary condition of the global model.
Figure 7.19 The final deformation of the global model.
Figure 7.20 SF1 of the pipeline.
Figure 7.21 SF2 of the pipeline.
Figure 7.22 SF3 of the pipeline.
Figure 7.23 A picked path for the pipeline.
Figure 7.24 SF1 along the path.
Figure 7.25 Contour plot of SM2 along the path.
Figure 7.26 SM2 along the path.
Figure 7.27 Contour plot of SM3 along the path.
Figure 7.28 SM3 along the path.
Figure 7.29 SF1 along the path in different coiling drum diameter.
Figure 7.30 SM3 along the path in different coiling drum diameter.
Figure 7.31 SM2 along the path in different coiling drum diameter.
Figure 7.32 SF1 along the path in different sinking distance.
Figure 7.33 SM3 along the path in different sinking distance.
Figure 7.34 SM2 along the path in different sinking distance.
Figure 7.35 SF1 along the path in different reeling length.
Figure 7.36 SM3 along the path in different reeling length.
Figure 7.37 SM2 along the path in different reeling length.
Figure 7.38 The defined distance.
Figure 7.39 SF1 along the path in different location of the bearing plate.
Figure 7.40 SM3 along the path in different location of the bearing plate.
Figure 7.41 SM2 along the path in different location of the bearing plate.
Chapter 8
Figure 8.1 Bonded flexible pipe (Antal et al., 2003) [1].
Figure 8.2 Production and gas lif hoses on the Heidrun TLP (Antal et al., 2003) ...
Figure 8.3 Typical cross-section of an unbonded flexible pipe (Zhang et al., 200...
Figure 8.4 General arrangement for local curvature analysis at the bellmouth or ...
Figure 8.5 Mooring and riser system design (Seymour et al., 2003) [7].
Figure 8.6 Overview of riser system interface design (Seymour et al., 2003) [7].
Figure 8.7 Water injection flexible pipe technology limits (Remery et al., 2004)...
Chapter 9
Figure 9.1 Flexible riser configurations.
[1]
Figure 9.2 Configuration of lazy-wave riser.
Figure 9.3 Lazy-wave riser configuration.
Figure 9.4 Force sketch of a differential element of suspended riser.
Figure 9.5 Force sketch of a differential element of boundary-layer segment.
Figure 9.6 Force sketch of a differential element of riser laid on seabed.
Figure 9.7 Flow chart of numerical calculation.
Figure 9.8 Sketch of OrcaFlex Model.
Figure 9.9 Comparison of lazy-wave configurations.
Figure 9.10 Comparison of lazy-wave tensions.
Figure 9.11 (a) Comparison of lazy-wave bending moments. (b) Comparison of bendi...
Figure 9.12 (a) Comparison of lazy-wave shears. (b) Comparison of shears in TDP.
Figure 9.13 Bending moment with the variation os seabed.
Figure 9.14 Shear with the variation of seabed.
Figure 9.15 Inclination angle at TDP with the variation of seabed stiffness.
Figure 9.16 Maximum embedment with the variation of seabed stiffness.
Figure 9.17 Lazy-wave configuration with the variation of hang-off inclination a...
Figure 9.18 Tension with the variation of hang-off inclination angle.
Figure 9.19 Bending moment with the variation of hang-off inclination angle.
Figure 9.20 Shear with the variation of hang- off inclination angle.
Figure 9.21 Lazy-wave configuration with the variation of buoyancy section lengt...
Figure 9.22 Tension with the variation of buoyancy section length.
Figure 9.23 Bending moment with the variation of buoyancy section length.
Figure 9.24 Shear with the variation of buoyancy section length.
Chapter 10
Figure 10.1 Configuration of steep wave riser.
Figure 10.2 Steep wave riser configuration.
Figure 10.3 Forces acting on the touch-down segment.
Figure 10.4 Forces acting on the touch-down segment.
Figure 10.5 Flow chart of numerical calculation.
Figure 10.6 Comparison of steep-wave configurations.
Figure 10.7 Comparison of steep-wave tensions.
Figure 10.8 Comparison of steep-wave bending moments.
Figure 10.9 Comparison of steep-wave shear forces.
Figure 10.10 Comparison of steep-wave shears near DP.
Figure 10.11 Comparison of steep-wave shears near LP.
Figure 10.12 Steep wave configuration with the variation of buoyancy segment’s e...
Figure 10.13 Tension with the variation of buoyancy segment’s equivalent outer d...
Figure 10.14 Bending moment with the variation of buoyancy segment’s equivalent ...
Figure 10.15 Shear force vs. buoyancy equivalent outer diameter.
Figure 10.16 Steep wave configuration with the variation of buoyancy segment len...
Figure 10.17 Tension with the variation of buoyancy segment length.
Figure 10.18 Bending moment with the variation of buoyancy segment length.
Figure 10.19 Shear force with the variation of buoyancy segment length.
Figure 10.20 Steep wave configuration with the variation of buoyancy segment loc...
Figure 10.21 Tension vs. buoyancy segment location.
Figure 10.22 Bending moment vs. buoyancy segment location.
Figure 10.23 Shear force vs. buoyancy segment location.
Figure 10.24 Steep wave configuration vs. current velocity.
Figure 10.25 Tension vs. current velocity.
Figure 10.26 Bending moment vs. current velocity.
Figure 10.27 Shear force with the variation of current velocity.
Chapter 11
Figure 11.1 Typical unbonded flexible pipe wall structure
[1].
Figure 11.2 Global analysis model of unbonded flexible pipe.
Figure 11.3 Illustration for node variables: (a) uin; (b) .
Figure 11.4 Hysteretic bending stiffness curve (Péronne et al., 2015).
Figure 11.5 Parallelogram hysteresis loop (Zhang et al., 2008).
Figure 11.6 Bend stiffener schematic diagram.
Figure 11.7 Winkler foundation model.
Figure 11.8 Bending hysteresis loop.
Figure 11.9 Bend stiffener profile.
Figure 11.10 Unbonded flexible riser configuration.
Figure 11.11 Effective tension along arc length.
Figure 11.12 Curvature along arc length.
Figure 11.13 Declination angle along arc length.
Figure 11.14 Time history response of top effective tension.
Figure 11.15 Time history response of curvatures at bend stiffener’s root end.
Figure 11.16 Time history response of curvatures at bend stiffener’s tip end.
Figure 11.17 Time history response of maximum curvature in TDZ.
Figure 11.18 Bending moment vs. curvature in TDZ.
Figure 11.19 Effective tension vs. effective bending stiffness in TDZ.
Figure 11.20 Time history response of vertical displacement at static TDP.
Figure 11.21 Time history response of effective tension at static TDP.
Figure 11.22 Static/dynamic response with different top connection conditions.
Figure 11.23 Static/dynamic response with different bending behaviors.
Figure 11.24 Static/dynamic response with different top angles.
Chapter 12
Figure 12.1 The constitution of the towed system.
Figure 12.2 Plan view of circle maneuver in towed system.
Figure 12.3 Curves of vehicle depth in reference [8].
Figure 12.4 Curves of vehicle depth of my simulation model in OrcaFlex.
Figure 12.5 The configuration of the towed cable of reference [8] in OrcaFlex.
Figure 12.6 Plan view of circle maneuver.
Figure 12.7 Depth variation of the towed body.
Figure 12.8 Tension variation of the towed end.
Figure 12.9 Depth variation of the towed body with the change of the diameter of...
Figure 12.10 Maximum tension variation of the towed body with the change of the ...
Figure 12.11 Maximum tension variation of Ct (Cn = 1.44).
Figure 12.12 Maximum tension variation of Cn (Ct = 0.015).
Figure 12.13 Depth variation of towed body with Ct (Cn = 1.44).
Figure 12.14 Depth variation of towed body with Cn (Ct = 0.015).
Figure 12.15 Distribution of tension along the length direction of the 300-m cab...
Figure 12.16 Distribution of tension along the length direction of the 300-m cab...
Chapter 13
Figure 13.1 Load analysis of pipeline.
Figure 13.2 Schematic diagram of lumped mass method.
Figure 13.3 Schematic diagram of contact relationship for cable-cable.
Figure 13.4 Schematic diagram of umbilical cable.
Figure 13.5 Schematic diagram of the model.
Figure 13.6 The distribution of the clashing force for interference.
Figure 13.7 The distribution of the effective tension under interference.
Figure 13.8 The distribution of the curvature of the umbilical cable under inter...
Figure 13.9 The distribution of standard deviation of the curvature of the umbil...
Figure 13.10 The distribution of the bending moment of the umbilical cable under...
Figure 13.11 The distribution of the curvature and bending behavior of the riser...
Chapter 14
Figure 14.1 Bending stiffener and bellmouth.
Figure 14.2 Global configuration of flexible pipe.
Figure 14.3 Load model of flexible pipe.
Figure 14.4 Cross section of helical strip.
Figure 14.5 Bending hysteresis model of flexible pipe.
Figure 14.6 S-N curve for high strength steel.
Figure 14.7 Comparison between Goodman’s and Gerber’s theory.
Figure 14.8 Schematic of bending stiffener.
Figure 14.9 Results of global analysis.
Figure 14.10 Time history response of pipe tension.
Figure 14.11 Time history response of pipe bending curvature.
Figure 14.12 Time history response of stress of helical strip at top point.
Figure 14.13 Results of global analysis.
Chapter 15
Figure 15.1 Umbilical cross-section (Bjornstad, 2004).
Figure 15.2 IPU dynamic cross-section, super duplex flowline (Heggadal, 2004).
Figure 15.3 Diagram of deformations during fabrication and installation.
Chapter 16
Figure 16.1 Schematic of helical geometry.
Figure 16.2 Time history of friction stress for increased tension model.
Figure 16.3 Stress behavior of STU versus SCR.
Figure 16.4 FPSO/STU system layout.
Figure 16.5 STU layup.
Figure 16.6 Outer tube friction forces.
Chapter 17
Figure 17.1 Simplified umbilical model with winding angle.
Chapter 18
Figure 18.1 Example of subsea umbilical cable structure [1].
Figure 18.2 Design flowchart of umbilical cable cross-section [2].
Figure 18.3 Design flowchart of umbilical cable cross-section [3].
Chapter 19
Figure 19.1 External pressure testing system.
Figure 19.2 Testing specimens after buckling.
Figure 19.3 Representative volume unit of reinforced layer.
Figure 19.4 Cross-section of FGRFP.
Figure 19.5 The flow chart of Matlab program.
Figure 19.6 Ovality-external pressure curve of FGRFP by using numerical analysis...
Figure 19.7 First buckling mode of FGRFP subjected external pressure.
Figure 19.8 The curve of external pressure and node displacement at the top of p...
Figure 19.9 The curve of external pressure and node displacement at the waist of...
Figure 19.10 Diagrammatic drawing for the imperfection’s location.
Figure 19.11 The stress nephogram of FGRFP.
Figure 19.12 The stress curve at top and waist of pipe’s cross-section change wi...
Chapter 20
Figure 20.1 Typical Construction of FGRFP.
Figure 20.2 The curves of burst pressure and time.
Figure 20.3 FEM of FGRFP.
Figure 20.4 Boundary conditions of FGRFP under internal pressure.
Figure 20.5 Axial stress distributions of each layer under internal pressure.
Figure 20.6 Global and local coordinate systems.
Figure 20.7 Axial stress-pressure curve of inner fiber glass reinforced layer (a...
Figure 20.8 Axial stress-pressure curve of each layer.
Figure 20.9 Effect of winding angle on internal pressure.
Figure 20.10 Effect of winding angle on hoop strain and axial strain.
Figure 20.11 Effect of D/t ratio on internal pressure.
Chapter 21
Figure 21.1 Construction of FGRFP.
Figure 21.2 Cross-section of FGRFP.
Figure 21.3 Tensile test of the specimen in process.
Figure 21.4 Stress-strain data of HDPE from tensile test.
Figure 21.5 Failure mode of the specimen.
Figure 21.6 Tension-extension relation of three specimens.
Figure 21.7 Treatment of reinforced layers
Figure 21.8 Interaction force between layers.
Figure 21.9 Pipe model in FEM.
Figure 21.10 Network of fiberglass in FEM.
Figure 21.11 Equivalent cross-section.
Figure 21.12 Tension-extension relation from three methods.
Figure 21.13 Deformation of FGRFP after extension.
Figure 21.14 Radius-extension relation (analytical model and FE model).
Figure 21.15 Fiberglass stress variation in different layers (FE model).
Figure 21.16 Tension-extension relation of each material (analytical model).
Figure 21.17 Comparison between pure PE pipe and FGRFP with the same thickness (...
Figure 21.18 The unwinding process of fiberglass (FE model).
Figure 21.19 Tension-extension relation of each material in different winding an...
Figure 21.20 Contribution of each material in different winding angles (analytic...
Figure 21.21 Tension-extension relation of each material in different fiberglass...
Figure 21.22 Tension-extension relation of each material in different diameter-t...
Chapter 22
Figure 22.1 Structure of FRFP.
Figure 22.2 Stress-strain curve from tensile test.
Figure 22.3 The four-point facility.
Figure 22.4 Diagrammatic sketch of facility.
Figure 22.5 The four-point facility.
Figure 22.6 Bending deformation of three specimens.
Figure 22.7 Curvature-moment curves of three test specimens.
Figure 22.8 Simplification of reinforced layer.
Figure 22.9 The FEM model of FRFP.
Figure 22.10 Boundary condition of the FEM model.
Figure 22.11 Comparison of results from bending test, theoretical method, and nu...
Figure 22.12 Stress distribution in FEM simulation.
Figure 22.13 Effect of wall-thickness.
Figure 22.14 Effect of Δ0.
Chapter 23
Figure 23.1 Structure of FRFP.
Figure 23.2 Torsion deformation of three specimens.
Figure 23.3 The cross-section in the bulge area of Specimen 2.
Figure 23.4 The cross-section in the bulge area of Specimen 3.
Figure 23.5 The damage of reinforced layers of Specimen 1 after parting from out...
Figure 23.6 Torque-torsion angle curves of three test specimens.
Figure 23.7 Cylindrical coordinate system.
Figure 23.8 Relationship between on-axis coordinate (L, T, r) and off-axis coord...
Figure 23.9 Front view of FRFP.
Figure 23.10 Side view of FRFP.
Figure 23.11 Discrete field of one layer before aligning orientation.
Figure 23.12 Discrete field of one layer after aligning orientation.
Figure 23.13 Deformation and von Mises stress distribution.
Figure 23.14 Torque-torsion angle relationship of three methods.
Figure 23.15 Torque-torsion angel relations under different winding angles.
Figure 23.16 Torque-torsion angel relations under different reinforced layer thi...
Figure 23.17 Torque-torsion angel relations under different radius-thickness rat...
Chapter 24
Figure 24.1 Schematic diagram of pipeline structure.
Chapter 25
Figure 25.1 FGRFP tension time histories.
Figure 25.2 FGRFP bending moment time histories.
Figure 25.3 Rain flow histogram of tension.
Figure 25.4 Rain flow histogram of bending moment.
Figure 25.5 Stress nephogram.
Figure 25.6 Stress time histories of inner PE layer and outer PE layer.
Figure 25.7 Stress time histories of all structural layers. The mean stress of t...
Figure 25.8 Stress of 55° layers.
Figure 25.9 Stress of −55° layers.
Figure 25.10 Comparison of 55° layer and −55° layer (0.75 mm).
Figure 25.11 Stress comparison of PE layer under different thickness of fibergla...
Figure 25.12 Comparison of 55° layer and −55° layer (0.5 mm).
Figure 25.13 Comparison of 55° layer and −55° layer (0.25 mm).
Figure 25.14 Stress contrast of reinforcement layer under different thicknesses.
Figure 25.15 S-N Curve of FGRFP.
Chapter 26
Figure 26.1 Typical flexible riser structure.
Figure 26.2 Drawing of FMC end-fitting.
Figure 26.3 Interlock structure of carcass.
Figure 26.4 Inner liner expander.
Figure 26.5 Carcass under external pressure.
Figure 26.6 Deformation of carcass during pressure cycling.
Figure 26.7 P
c
and δ
car
relationship for different carcass profiles and pipe siz...
Chapter 27
Figure 27.1 An example of a bend stiffener.
Figure 27.2 Local response model.
Figure 27.3 Extreme load description.
Figure 27.4 Load contour.
Figure 27.5 Capacity curve and bend stiffener performance.
Figure 27.6 Bend stiffener geometry.
Figure 27.7 Bend stiffener performance.
Figure 27.8 Design chart for bend stiffener.
Chapter 28
Figure 28.1 Steel tube umbilical or thermoplastic umbilical with spool [1].
Figure 28.2 Thermoplastic umbilical [1].
Figure 28.3 Thermoplastic umbilical [3].
Figure 28.4 Thermoplastic umbilical [4].
Figure 28.5 Thermoplastic umbilical [5].
Figure 28.6 Thermoplastic Umbilical [7].
Chapter 29
Figure 29.1 Degrees of freedom of floating structures.
Figure 29.2 The static state of the pipeline under a water depth of 150 m.
Figure 29.3 The static state of pipelines at different lay angles.
Figure 29.4 Top tension at different lay angles.
Figure 29.5 Top tension at different water depths.
Figure 29.6 Wave direction distribution.
Figure 29.7 Maximum tension at a lay angle of 70°.
Figure 29.8 Minimum tension at a lay angle of 70°.
Figure 29.9 Minimum bending radius at a lay angle of 70°.
Figure 29.10 Maximum tension at the lay angle of 80°.
Figure 29.11 Minimum tension at the lay angle of 80°.
Figure 29.12 Minimum bending radius at a lay angle of 80°.
Figure 29.13 The relationship between the minimum bending radius and the submerg...
List of Tables
Chapter 2
Table 2.1 Interlocked carcass cross-section parameters.
Table 2.2 Interlocked carcass parameters.
Table 2.3 Collapse pressures.
Table 2.4 SSRTP-1 parameters.
Table 2.5 SSRTP-2 parameters.
Table 2.6 Collapse pressures.
Chapter 3
Table 3.1 Geometric and material parameters of FEM.
Table 3.2 Pressure armor layer geometrical properties.
Table 3.3 Steel strip geometrical properties.
Table 3.4 Models with different inner radius.
Table 3.5 Prediction by two theoretical models.
Chapter 4
Table 4.1 Parameters for pressure armor layer.
Table 4.2 Pipe’s parameters.
Chapter 5
Table 5.1 Design requirements.
Table 5.2 Geometrical parameters.
Table 5.3 Material parameters.
Table 5.4 Utilization factors for flexible pipe.
Table 5.5 Load cases.
Table 5.6 Maximum stresses and strains summary by layers.
Table 5.7 Comparison between theoretical and FEM results.
Chapter 7
Table 7.1 The maximum SM3 and SM2 in different coiling drum diameter.
Table 7.2 The maximum SM3 in different sinking distance.
Table 7.3 The maximum SM3 in different reeling length.
Table 7.4 The maximum SM3 of each case.
Chapter 9
Table 9.1 Riser parameters.
Table 9.2 Other environmental parameters.
Table 9.3 Result comparisons of analytical model and FEM by OrcaFlex.
Table 9.4 Result comparisons in TDP area.
Chapter 10
Table 10.1 Flexible riser parameters.
Table 10.2 Environmental parameters.
Table 10.3 Results of numerical method vs. FEM by OrcaFlex.
Chapter 11
Table 11.1 Unbonded flexible pipe parameters.
Table 11.2 Environment and hydrodynamic coefficients.
Table 11.3 Static result comparisons.
Chapter 12
Table 12.1 Physical parameters of the towed cable.
Table 12.2 Physical parameters of the towed body.
Chapter 14
Table 14.1 Wave scatter diagram.
Table 14.2 Stochastic wave load.
Table 14.3 Input parameters of flexible pipe.
Table 14.4 Input parameters of hydrodynamic coefficient.
Chapter 16
Table 16.1 STU layup data.
Table 16.2 Comparing different STU fatigue approaches.
Table 16.3 Comparing base case to sensitivities—all time domain.
Chapter 19
Table 19.1 Dimension of specimens.
Table 19.2 The results of external pressure test.
Table 19.3 Dimension of FRGFP.
Table 19.4 Material parameters of FGRFP.
Chapter 20
Table 20.1 Geometric parameters of testing specimens.
Table 20.2 Material properties of each layer.
Table 20.3 Burst pressure of the testing specimen.
Table 20.4 Comparison of three methods.
Chapter 21
Table 21.1 Specifications of the tensile test specimen.
Table 21.2 Geometric parameters of the tensile test specimen.
Table 21.3 Material properties of FGRFP.
Table 21.4 Ultimate tensile strength (kN).
Table 21.5 Different diameter-thickness ratios of FGRFP.
Chapter 22
Table 22.1 Dimensions of test facility.
Table 22.2 Material properties of testing specimens.
Table 22.3 Geometric parameters of testing specimens.
Table 22.4 Valid length and diameter of specimens.
Table 22.5 Summary of bending test data.
Chapter 23
Table 23.1 Material properties of testing specimens.
Table 23.2 Geometric parameters of testing specimens.
Table 23.3 Valid length and diameter and diameter of specimens.
Table 23.4 Elastic constants of reinforced layers.
Chapter 24
Table 24.1 Long-term hydrostatic pressure reduction factor for composite pipes a...
Chapter 25
Table 25.1 Size parameters of EGRFP.
Table 25.2 Material parameters of EGRFP.
Table 25.3 Environmental parameters.
Table 25.4 Specific Parameters of the layer.
Chapter 26
Table 26.1 Carcass properties.
Table 26.2 Maximum possible contact pressure.
Chapter 27
Table 27.1 Non-dimensional parameters.
Chapter 29
Table 29.1 Pipe parameters.
Table 29.2 Static analysis of flexible laying.
Table 29.3 Top tension at different lay angles.
Table 29.4 Top tension at different water depths.
Table 29.5 Wave environmental parameters.
Table 29.6 Ocean current parameters.
Table 29.7 Dynamic response results in different wave directions.
Table 29.8 Dynamic response results with a lay angle of 80°.
Table 29.9 Sensitivity analysis results of different submerged weights.
Guide
Cover
Table of Contents
Title page
Copyright
Preface
Acknowledgment
About the Author
Begin Reading
Index
Also of Interest
End User License Agreement
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Scrivener Publishing
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Publishers at Scrivener
Martin Scrivener ([email protected])
Phillip Carmical ([email protected])
Deepwater Flexible Risers and Pipelines
Yong Bai
This edition first published 2021 by John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, USA and Scrivener Publishing LLC, 100 Cummings Center, Suite 541J, Beverly, MA 01915, USA
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Library of Congress Cataloging-in-Publication Data
ISBN 9781119322726
Cover design by Kris Hackerott
Set in size of 11pt and Minion Pro by Manila Typesetting Company, Makati, Philippines
Printed in the USA
10 9 8 7 6 5 4 3 2 1
Preface
Deepwater flexible risers and pipelines are challenges for deepwater oil and gas productions. This is particularly important when we use FPSO and semi-submersible solutions. In the Gulf of Mexico, deepwater flexible risers and pipelines are also widely used for tie-in of new production wells and manifolds to existing production systems such as TLPs and Spars, etc.
The author has been fortunately involved with deepwater flexible risers and pipelines projects when he was working in the USA and Norway. In the past 15 years, he has been engaged in research and consulting of relevant subjects. This book summarizes his work in four different subject areas:
Part I deals with mechanics of deepwater risers where our focus is cross-section design of the risers under combined loads. We derived formulation for strength analysis of deepwater flexible pipes under internal pressure, external pressure, tension, torsion, and bending curvatures. We also address strength of the pipe during coiling, installation, and possible failure during the process.
Part II addresses global response of the riser systems in deepwater. We derived formulations for static configuration design and dynamic response. This is particularly important for global configuration design in static and dynamic environment.
Part III is devoted to a new kind of flexible pipe that is made of fiberglass material. We derived formations for pipes under internal pressure, external pressure, tension, bending, and torsion.
Part IV summarizes experience we have for ancillary equipment design. This is mainly for riser hang-off locations and touch down areas. We address the design of bending stiffeners, bend restrictors and connectors. Riser connectors are perhaps the single most critical element in the safety and integrity of the riser and pipeline systems.
We wish that this book will be a useful reference source of flexible risers and pipelines design and analysis for subsea engineers. This book mainly considers deepwater water applications. For shallow applications, we recommend our book “Flexible Pipelines and Power Cables”. For cross-sectional design, we recommend our book entitled “Flexible Pipes”. All three books are published by Scrivener Publishing and Wiley.
Acknowledgment
The authors would like to appreciate Prof. Yong Bai’s graduate students and post-doctoral fellows at Zhejiang University who provided the initial technical writing for Chapters 2, 3, and 4 (Fancesco Cornacchia, Qiangqiang Shao, and Dr. Ting Liu), Chapter 6 (Dr. Yutian Lu), Chapter 7 (Dr. Yuxin Xu and Dr. Pan Fang). Chapters 9 to 11 (Dr. Weidong Ruan), Chapters 12 and 13 (Dr. DaPeng Zhang), Chapters 14 (Dr. KA Jiamg), Chapters 17 and 18 (Dr. Wei Qin), Chapter 19 (Dr. XiaoJie Zhang), Chapter 20 (Dr. Shanying Lin), Chapter 21 (Dr. Yuxin Xu), Chapter 22 (Dr. Yifan Gao), Chapter 23 (Ms. Xinyu Sun), Chapter 24 (Dr. Mohsen Saneian), Chapters 25 to 26 (Dr. Wei Qin) Chapter 29 (Dr. Zhao Wamg). Thanks to all persons involved in reviewing this book. The authors also would like to thank the flexible pipe manufacturing company OPR Inc. for their support for publishing this book.
The author is grateful to Ms. Xin Zhou who provided editorial assistance. I am thankful to Martin Scrivener and Phillip Carmical of the Scrivener Publishing and Wiley.
Prof. Yong BaiJune 01, 2020
About the Author
Professor Yong Bai is the president of Offshore Pipelines and Risers Inc. and also the director of the Offshore Engineering Research Center at Zhejiang University. He has previously taught at the University of Stavanger in Norway where he was a professor of offshore structures. He has also worked with ABS as manager of the Offshore Technology Department and DNV as a JIP project manager.
Professor Yong Bai has also worked for Shell International E&P as a staff engineer. Through working at JP Kenny as manager of advanced engineering and at MCS as vice president of engineering, he has contributed to the advancement of methods and tools for the design and analysis of subsea pipelines and risers.
Professor Bai is the author of approximately 10 books such as “Marine Structural Design” and “Subsea Pipelines and Risers”. He authored more than 100 SCI and EI papers on the design and installation of subsea pipelines and risers.
Part 1LOCAL ANALYSIS
1Introduction
1.1 Flexible Pipelines Overview
The oil and gas industry proclaims pipelines as the most economical device of large scale overland conveyance for crude oil and natural gas, compared to truck and rail transportation. These can continuously carry large quantities of fluids and they are considered by far to be the most reliable. The rapid development of the petroleum industry leads to high financial investments in engineering research, which has quickly conducted to achievement of remarkable effects, so that recently steel homogeneous pipes have been replaced by flexible pipelines, widely used by oil and gas industry for both onshore and offshore purposes. Mostly, they are employed offshore as transportation of well products such as oil, gas, and condensate, well control lines, injection of water and gases, and export of processed product, but also as flowlines connecting subsea wells, well-head platforms, templates or loading terminals, processing platforms, and jumper lines connecting fixed platforms to support vessels.
Flexible pipelines are relatively new kinds of profiles which have developed since the late 1970s; initially, they were used in few offshore areas until being employed in many projects, thanks to the applicability in water depths up to 8,000 ft, pressures up to 10,000 psi, and high temperatures up to 150°, beside the high adaptability to different environmental conditions and large vessels motion [1].
Nowadays, even if many researchers are employed to enhance knowledge about flexible pipelines, there are no books available that systematically introduce the design procedures and analysis criteria that are always valid for the wide spectrum of these structures. On the other hand, it is possible to find many reference sources which can streamline the issues.
Moreover, they are widely used also because of their easy and cheap transport and installation, due to the possibility of being prefabricated onshore in long lengths and stored in limited size on reels; in fact, as most relevant structural property, these pipes show very low bending stiffness in comparison to axial tensile stiffness. Besides, the economic benefits, they are considered to be technically proficient due to their easy and fast laying procedure, durability, and recoverability. In the light of the above, the petroleum industry turns into flexible structures, allowing for permanent connection between the subsea system and any facility at the water surface with large motions.
Being flexible pipes, crucial elements for the right operational oil and gas spill in terms of both performance and pollution, at the same time, a deep finite element model (FEM) is highly recommended in order to verify the reliability of the design. This method called DTA (Design Through Analysis) involves both the abovementioned procedures and the two-step process is used in complementary way in order to reach less conservative outcomes in designing, thus minimizing the project CAPEX (Capital Expenditure) and OPEX (Operating Expenditure). In some cases, it shows that codes and regulations are over conservative, and the real behavior can be captured through a FE simulation when the input parameters are well defined, if not data are statistically modeled in order to produce a reliable distribution for a range of loads and effects.
1.2 Environmental Conditions
The wide expansion of these structures during the last decades has been made possible thanks to the costs-design optimization. It considers a deep understanding of the environmental conditions in which the pipeline will be installed and operated. Some of the drivers are: water depth and oceanographic data, chemical composition and flow phase of the extracted fluid, quantity of salt in the surrounding water, and operating internal and external temperatures and pressure. In addition, transport and installation circumstances must be considered due to the fact that in some cases, extreme loading conditions are shown during these phases. Most of the time, combination of loads needs to be taken into account. The analysis of the surrounding conditions, for example, temperature and corrosion, cannot be under estimation because of limiting capacity of the structures.
Temperature can affect the correct purpose of the pipe, in some cases, very high or low temperature of the fluids leads to the need of extra thermal insulation design, such as pipe-in-pipe or wet insulation, which considers the different thermal responses of materials. Polymeric materials exhibit lower thermal conductivity and higher thermal expansion coefficients compared to steel, so that the plastic layers govern the temperature profile through the pipe wall. Operating temperature is the foremost principle for selecting the polymer material in order to ensure the correct mechanical behavior of the pipe. In fact, for a given material, as the temperature rises the magnitude of the yield stress and Young modulus decreases, so the ultimate strain increases and vice versa, leading to various mechanical response properties during the service life of the structures. Generally, temperature profile impacts most of the design parameters, it is also influenced by the water depth outwardly and by the reservoir formation internally; thus, it must be carefully considered for both service limit state and ultimate limit state.
Cross-sectional integrity needs to be mentioned for a remarkable pipeline design, which is of relevant importance especially for deep water. In fact, here hydro-static pressure is high, and the cross-section must be dimensioned against local buckling failure which is extremely influenced by imperfections. Not only, any other steel components provide structural support against axial, bending, and torsional loads, and their integrity is essential. Corrosion and cracks damages are hard to detect, being the structural profile made by different layers. Considering the conservative but actual hypothesis of failure of polymeric materials, steel corrosion is caused by interaction with salt water, air, or internal acid fluids or combination of them, which chemically alter materials. Besides the mechanical properties and price, the main driver for the selection of steel materials is the corrosion resistance to operating environment. The annulus conditions are continuously tested and monitored, and it is common practice to include deterioration protections such as coating, corrosion inhibitors, application of special materials and cathodic protection, in addition to lubrication oil distributed along the pipe during the manufacturing.
During the years, the availability of reservoirs onshore and in shallow water has decreased, and the need of petroleum pushed the industry to open new challenging offshore campaigns. The employment of flexible pipes in subsea brings researchers to focus on the estimation of the structural behavior in deep waters. Here, the environmental conditions are tougher, and reinforcements are necessary. Hydro-static pressure rises as water depth increases, which leads to considerable hoop stresses and buckling issues. For the whole pipe, this problem is managed making use of devices that enhance the strength in this sense, but at the same time, they bring additional structural weight and increasing gravity loads. Now, it can be deduced that as the water column grows, the magnitude of the tensile load rises. Dynamic tension is amplified by existing drag forces if considering the substantial pipe length in deep water, which is directly reflected on the end fitting, with consequently fatigue damages at this point due to constraint effects that may take place.
What being said, the challenge of the engineering is trying to make the best design, keeping the costs as low as possible, moving from local to global analysis. Any structure needs a particular design for the specific field and for precise environmental conditions, at the same time taking advantages from the experiences about other projects. The selection of the most suitable setup for any flexible structure is founded on practice and engineering judgment, in Figure 1.1, some examples of possible riser configurations using flexible pipes for which the choice is based on the abovementioned principles [2–4].
Figure 1.1 Employment of flexible pipelines as risers.
1.3 Flexible Pipeline Geometry
Even if flexible pipelines have many applications, the common factor is to provide large flexural deformations while they are subjected to other loading forces, strictly necessary during installation and transport. Mostly, this property depends on their geometrical configuration, which is made by many layers. Generally, flexible pipes are compound by many main layers of different materials and functions:
Internal polymeric sealing layer provides insulation from internal fluids, prevents corrosion and leakage due to extract materials,
Helical armoring layers provide the required strength against different loading conditions, the number of layers and wires per each layer is variable and depends on the design;
Outer polymeric layer prevents seawater from interacting with the armor layers.
They can be characterized in two main groups: the metal-based flexible pipes designed to withstand high loads see Figure 1.2 and the composite-based flexible pipes (FCP), which are much simpler and employed for lower functional requirements. These can be further divided in two more groups: bonded and unbonded structures.
In the bonded structures, all the elements are fused together in the surrounding matrix through a vulcanization process.
Figure 1.2 Unbonded composite-based flexible pipe.
This work is focused on unbonded type, i.e., when layers are not connected into a single structure, but each component makes up a cylindrical layer that is able to slide relatively to the other layers. Composite-based unbonded flexible pipes are defined as the base-case for this work and, basically, are composed by an innermost thermoplastic layer called liner made of polyester material that surrounds the collected material. Two (or four) layers of carbon steel material strip reinforcements, adjacently, spirally wounded around the outer surface of the innermost cylinder at an opposite lay angle of about 55°, one by one (or two by two) to withstand torque loading. This profile must provide mainly support against tensile loads. Finally, an outermost polymeric sheath to prevent contamination from the external environment.
On the other hand, metal-based unbonded flexible pipes are suitable for static and dynamic applications with length of several hundred meters; they are compound by nine layers with different functions. The interlocked metal carcass layer and the pressure armor layer are added in the profile with respect to the unbonded FCP. The first is needed to prevent the collapse due to high hydro static pressure or sudden depressurization of internal fluids and also to avoid erosion from the extracted materials; the second provides strength against high hoop stresses due to internal and external pressure. Also, the tensile strength is improved, substituting strips with wires, which show wider cross-sectional dimensions.
A further division among unbonded pipelines is made considering the presence of the steel carcass supporting the inner liner: if it is included in the design, the pipe can be named rough bore; if not, it is a smooth bore structure see Figure 1.3.
Figure 1.3 Unbonded metal-based flexible pipe.
Other elements, such as anti-wear and bird-caging tapes, can be considered as non-structural, but they are very relevant in designing because they rule the flow and the contacts, which can modify the properties of the structural elements.
1.4 Base Case-Failure Modes and Design Criteria
API Recommended Practice 17B is the guideline to follow in order to have a proficient design. Any pipelines must satisfy code requirements under the actual environmental conditions, beyond which it is not suitable anymore for its purpose. In order to do so, different types of load and failure modes must be considered.
Failure is not necessary considered as a structural limit, but it can be easily defined as a modification of the flow conditions within the pipe, in fact leakage and reduction of internal cross-section undermine the main achievement of the structure.
Unbonded composite-based are weaker than metal-based flexible pipes and, in many cases, are not the best choice for deep water. However, a list of all the possible pipe failure modes and mechanisms from the code, valid for both cases, is delivered below:
Collapse
Burst
Tensile failure
Compressive failure
Overbending
Torsional failure
Fatigue failure
Erosion
Corrosion
All the components are subjected to external loads and they have different reactions and strength, and in general, the effects increase as the water depth grows. Some failure mechanisms for specific elements appear as results of the failure mode due to loads for which they are not designed for. For composite unbonded pipelines, it is common that steel strips, which are designed for withstanding axial loads, may buckle under excessive hydro-static pressure or tensile loads, as well as during the transport phase.
If unbonded flexible pipes are subjected to axisymmetric loads, the stiffness has the same order of magnitude of steel pipes and they have linear behavior for tension, pressure, and torsion. Actually, hypothesis needs to be introduced to simulate the real response of the structure trying to keep the abovementioned configuration, for example, for local buckling imperfection are introduced symmetrically distributed along the cross-section.
It needs to be underlined that for weak pipes, such as FCP, the strength provided by internal and external plastic layers cannot be neglected.
A series of design criteria needs to be satisfied through strength reduction factors. When dealing with oil and gas problems, in particular off-shore, safety factors are very severe. For flexible pipes also, due to the very high uncertainties due to the complexity related to the helical shape of the steel layers, interactions, materials, and residual stresses, besides environmental forces, the safe margin must be considered wide enough. Design criteria express the safety for all the components; they are expressed in terms of allowable quantities which are specified by regulations and manufacturing, for:
Strain
Creep
Stress
Hydrostatic collapse
Mechanical collapse
Torsion
Crushing collapse and ovalization
Compression
Service life factors
