Development Targets FPS RISER DESIGN
West Africa Gulf of Mexico Brazil Voring Basin West of Shetland Others 600-2500m 1500-2500m 900-2000m 800-1500m 750-1500m
Dr Hugh Howells 2H Offshore Inc
OMAE, FPS in Harsh Environments Workshop Newfoundland Hotel, St Johns, July 1999
FPS Riser Design Challenges
Deep water
Weight, collapse
Riser Types
Vertically Tensioned
Spar, TLP, DDF
Severe currents
VIV fatigue, suppression devices large offsets
Flexible (up to 1000m, max 10 inch)
Simple and wave catenaries
Severe waves
large motions fatigue damage
Rigid Catenary (400m+, up to 30 inches)
Steel, titanium Simple, wave and bottom weighted
Insulation
Needed to prevent hydrate formation Increased drag
Free Standing
Hybrid bundles
Flexible Riser Applications
1600 1400 1200 1000 800 600
FPS Riser Applications
3000
Water Depth (m)
REQUIREMENTS FOR FUTURE DEVELOPMENTS Export Trunk Lines Export Feeder Lines Production Lines Service Lines Flexibles
2500 2000
Hybrid Steel Catenary
1500 1000 500
Flexible Risers
400
FLEXIBLES
200 0
10
12
14
16
18
20
22
24
26
28
Diameter Inches
30
12 16 20 24 Internal Diameter (inches)
28
32
Rigid Catenary Risers
Simple SCR Features
Extension to Pipeline Low Cost Mild environments Small vessel motions Small vessel offsets Large TDP motions TDP trenching
Vertical Section
Tether (3 Off) Pile Foundation
Flex Joint/Elbow and Weight Assembly Horizontal Section
Lazy Wave Catenary
Plan Length 0.75-1.5 Depth
Mean Top Angle 10-25 degrees
Simple Catenary
TDP Touch Down Point
800m 20 inch TLP SCR West of Shetlands
Vessel Motions
20.0
KEY: GoM TLP WoS
10.0
0.0
SEMI FPSO
-10.0
-20.0 -20.0
-10.0
0.0
10.0
20.0
SURGE (m)
TDP Buckling
Wave Catenary Riser Features
Buoyant Arch Higher Cost Large vessel motions Small TDP motions Harsh environments Large vessel offsets Complex installation
1200m 10 inch Wave Catenary West of Shetlands
Bottom Weighted Riser
Vertical Section
Flex Joint/Elbow and Weight Assembly Tether (3 Off) Horizontal Section Pile Foundation
Hybrid Risers
Vertical Bundle of Steel Pipes Syntactic and Air Can Offset or Non-Offset Flexible Jumpers 350m-3000m Water Depth FPSO, Barge, Semi
Offset and Non-Offset Hybrid Riser Arrangements
Hybrid Risers
Vertical Bundle of Steel Pipes Syntactic and Air Can Offset or Non-Offset Flexible Jumpers 350m-3000m Water Depth FPSO, Barge, Semi
Hybrid Riser Cross Section
Hybrid Riser Construction
Global Riser Analysis
Highly Dynamic & Non-Linear Response Time Domain FE Analysis
Flexcom, Riflex, ABAQUS
3 Dimensional Structure and Loading Numerous Load Cases Highly Iterative Analysis Intensive Uncertainties in seabed interaction
Simple SCR Extreme Stresses
28IN Simple Catenary Riser
Wave Catenary Extreme Stresses
28IN Buoyant Wave Riser
Extreme Hurricane Static/Dynamic von Mises stresses
1 0.9 0.8 0.7 von Mises/Yield 0.6
von Mises/Yield
Extreme Hurricane Dynamic and Static von Mises stresses
Optimised Configuration
1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0
0 500 Mod 1 Far Ex Mod 1 Far Static 1000 1500 Mod 2 Far Ex Mod 2 Far Static 2000 2500 Mod 3 Far Ex Mod 3 Far Static
Near Extreme Far Extreme Near Static Zero Static Far Static
0.5 0.4 0.3 0.2 0.1 0 3000 3500 Distance Along Riser From Vessel (m)
0.0
500.0
1000.0
1500.0
2000.0
2500.0
3000.0
3500.0 4000.0
4500.0
Distance Along Riser From Vessel (m)
Simple SCR First Order Fatigue
28in Simple Catenary Riser
Wave Catenary Fatigue
28in Buoyant Wave Catenary Riser
FIRST ORDER FATIGUE LIFE
FIRST ORDER FATIGUE LIFE 100000
100000 Unfactored Fatigue Life (years)
Unfactored Fatigue Life (years)
10000
10000
1000
1000
100
100
10
10
1 0
Dir 1
500
Dir 2 Dir 3
1000
Dir 4
1500
Dir 5 Dir 6
2000
Dir 7
2500
Dir 8 Min Life
3000
1 0 500 1000 1500 2000 2500 3000 3500 4000 Distance from Vessel (m)
Dir 1 Dir 2 Dir 3 Dir 4 Dir 5 Dir 6 Dir 7 Dir 8
Distance from Vessel (m)
Vortex Induced Vibration
High frequency stress reversals High fatigue damage rates Analysis using SHEAR7 and VIVA Many uncertainties in analysis methods
Catenary Riser VIV Fatigue
28in Simple Catenary Riser
VIV DAMAGE - TRANSVERSE CURRENTS
10 0.1 0.001 Fatigue Damage (Per Year) 1E-05 1E-07 1E-09 1E-11 1E-13 1E-15 1E-17
ACDSee GIF Image
1E-19 1E-21 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Location Along Riser from TDP (x/L) Bin 1 Bin 18 Bin 3 Bin 21 Bin 6 Bin 25 Bin 9 Total Bin 12 Bin 15
VIV Suppression
Strakes
Higher drag loading Higher stresses Higher pipe wall thickness Complex installation Higher cost
VIV Analysis Uncertainties
Changes in incidence angle along length Changes in structural properties Changes in diameter Non-monotonic current distribution Current direction variation with depth Seabed interaction Strake design and effectiveness Vessel motions and riser tension variation Wave loading
Fairings
better response, more expensive
How much suppression is needed?
Installation Issues
Weather windows - increased time, current Tension - limitation for large dia. lines Tow-out - fatigue damage VIV suppression - effect on method Reeled pipe - residual stresses
Reeled Installation
SCR Installation by Reel Vessel High Levels of Plastic Deformation (2%) Effect on Fatigue Performance ??
Thermal Insulation
Wax and hydrate prevention External coatings Pipe in Pipe - feasible as SCR? Heating (electrical or water circulation) Low weight in water Increased drag diameter Degraded response and worse VIV Increased cost
Riser Design Developments
STRIDE JIP
Steel Risers in Deepwater Environments
VIV response - tank and open water tests Riser-seabed interaction, testing and analysis Materials - fatigue of girth welds Installation - fatigue performance of reeled pipe
Conclusions (1/2)
FPS Riser Technology Developing- Not Mature Wide Range of SCR Applications
500m-3000m 4 - 30 diameter Mild - Harsh environments TLP - FPSO
Conclusions (2/2)
VIV understanding developing Reeled installation may be feasible Thermal insulation very important TDP and effects of trenching ?? Risers a key FPS technology
Low Cost Potential
