Riser Overview Lecture Feb 2011

MSc in Subsea Engineering

Overview of Riser Engineering Dr Patrick O’Brien Honorary Professor of Engineering, University of Aberdeen & Group Director, MCS Kenny

EG55F6 Risers Systems and Hydrodynamics


Presentation Overview 1.

Gene Genera rall C Con once cept pts s & Fiel Field d Lay Layou outt

2.

Ris Riser Syst Syste em Type Types s

3.

Over Overvi view ew of of Fund Fundam amen enta tals ls of of Rise Riserr Engineering

4.

Rise Riserr De Desi sign gn Co Cons nsid ider erat atio ions ns


1


Key Messages 

Dry tree tree vs wet tree: tree: Tensione Tensioned d vs Complian Compliantt



Riser T 



Riser Fundamentals 



es

TTRs, Flexibles, SCRs, Hybrids

Large displacement, effective tension, equations of motion, time vs frequency domain

Riser Design Considerations Considerations 

Vessel motions



Flexible pipe design issues and failure modes SCR design issues: touchdown and top connection flex/stress joint Internal flow regime and insulation Cross-section impact on global motions Coupled vessel-mooring-riser response

   



.

enera • •

oncep s

e

ayou

Dry Tree vs vs We Wet Tree Ten ensi sion oned ed vs Co Comp mpli lian antt


2


Riser System Selection RESERVOIR CONDITIONS

ENVIRONMENTAL CONDITIONS

PRODUCTION SCHEME

FIELD LAYOUT

SURFACE UNIT

RISER SYSTEM



System Sys tem Architecture: Architecture: Girassol Subs Subsea ea


3


Boomvang Nansen Fields



Two Main Riser Types 

“Dry Tree” riser “Wet Tree” riser



Preliminaries:





(Christmas) Tree ~ “manifold” type structure  

 

Point at which reservoir fluid is controlled “Head” of the well

Tree at seabed ~ “Wet” Tree Tree at sea surface ~ “Dry” Tree EG55F6 Risers Systems and Hydrodynamics

4


Feasibility of Dry or Wet Tree... 

“A riser should be vertical below wellhead (or ” 



If Dry tree riser... 



to allow equipment to be transmitted through the well

Riser must be vertical (from surface to seabed)

If Wet tree riser...  

No need to be vertical (from surface to seabed) Can connect directly to vessel (Slack in Riser) EG55F6 Risers Systems and Hydrodynamics


Dry vs Wet Tree Fundamentals 

How to cope with motions of vessel (Dry)  

Riser Su orted Verticall b buo anc cans Riser connected to vessel by Tensioners 



Riser top response decoupled from vessel motions 



Tensioners (like springs) extend and compress Vessel Heaves, riser doesn’t

How to cope with motions of vessel (Wet)  

Riser connected directly to vessel Enough slack/compliancy built into riser 

e.g. use of Wave shape configuration


5


Offshore Production Facility Types



Floating Production Vessel Types

FPSO Semi

Mini TLP

Deep draft

SPAR EG55F6 Risers Systems and Hydrodynamics

6


Independence Hub Semi

World’s deepest risers…2,438m

SCRs – 7 Initial - 9 Future

–STU



Technology Limits: Water Depth Deepest Semisubmersible

(Independence Hub approx 2,440m) (Nakika 1,920m)

Deepest TLP

(Magnolia approx 1,433m)

Deepest Spar

(Devil’s Tower approx 1,707m)


7


. • • •

ser ys em ypes Top Tensioned Risers (TTRs) Flexible Risers Steel Catenary Risers (SCRs) -



SPAR Top Tensioned Risers


8


SPAR Risers - Detail



Riser Top Tensioners (TLP)


9


Individual Riser Tensioners



Top Tension Riser Design


10


Dry vs Wet Tree Design • Must have dual independent barrier between uncontrolled reservoir fluid and environment – I.e. below wellhead 13 3/8 “ Outer Casing

• Dry Tree

Outer Annulus 9 5/8” Inner Casing

– Single or Dual Casing Riser

Inner Annulus

• (from Seabed to Surface)

5 ½” Production Tubing

• Wet Tree – No need (below wellhead = below seabed)



TTR Riser Design Issues 

What is the wall thickness of casings?  

, Extreme, fatigue, VIV loading

,

,..



How many cans/tensioners required to support the risers?



Tapered sections (reinforcements at seabed and vessel interfaces) EG55F6 Risers Systems and Hydrodynamics

11


Flexible Risers



Flexible Pipe Cross Section Example : Rough-bore Pipe (with Carcass)

Carcass (Stainless Steel) – External Pressure Resistance Carcass Profile:

Internal Sheath (Polymer) – Internal Fluid Containment Barrier

Pressure Armor (Carbon Steel) – Hoop Load Resistance Armor Profile:

Tensile Armor (Carbon Steel) – Tensile Load Resistance

External Sheath (Polymer) – External Fluid Barrier EG55F6 Risers Systems and Hydrodynamics

12


Flexible Riser Configurations FREE HANGING

LAZY WAVE

PLIANT WAVE®

STEEP S

STEEP WAVE

LAZY S



Bend Stiffeners 

Function  



Prevents over-bending Provides moment transition between flexible and rigid end connection

Design Considerations 

Steep Wave

Non-linear material properties

Interface arrangement 



Stiffener

Polyurethane fatigue and creep 



Bend

e.g. I-tubes, porch,

Manufacturing tolerances


13


Buoyancy Devices 

Types 

Distributed – lazy wave and steep wave configurations  



Configuration achieved by buoyancy modules Manufacturers include  Trelleborg CRP Ltd  Flotech  Emerson Cuming

Concentrated – lazy S and steep S configurations  

Confi uration achieved b tether buo Manufacturers include  Trelleborg CRP Ltd



Distributed Buoyancy 

Distributed   

 

Steep-wave Wave Pliant wave Floatation attached to result in desired riser configuration Buoyancy Supplied by discrete modules Clamps required for buoyancy module to make connection to pipe

Wave

Wave®


14


Distributed Buoyancy



Design considerations – Usually syntactic foam – Net buoyancy requirement

output from configuration design – Clamping

Module slippage can alter configuration – Gradual loss of buoyancy over time – Clashing



Distributed Buoyancy 

Buoyancy Module    

2 half shells Held in place by clamp Half shells strapped together over clamp Profiled to avoid


15


Distributed Buoyancy Issues • •

Numerical modeling of modules discrete or smeared Accountin for arameters that reduce buoyancy: – – – – –

•

•

Water absorption Initial elastic compression Creep Marine growth Manufacturing tolerances

Review of design requirements for 10% in API RP 17B Guidance on module spacing

Courtesy of Trelleborg CRP Ltd.



Concentrated Buoyancy 

Concentrated buoyancy  

Steep-S Laz -S Steep-S



Lazy-S

Design considerations  

Usually pressurized steel tanks Buoyancy requirement 



Compartmentalized buoyancy tanks 

 

ensure taut in all internal fluid conditions

Redundancy

Tether hold-down arrangement Gutter to prevent interference


16


Subsea Arch



Subsea Arch


17


Subsea Arches - Key Issues •

Redundancy for mid-water arches with buoyancy tanks in case of oo e an compar men – Depends on risk level i.e. production (oil) versus water service over midwater arch – Too much redundancy can be prohibitive – Tolerances – Arch Sizin – Installation issues

Courtesy of Trelleborg CRP Ltd.



Steel Catenary Risers


18


Steel Catenary Risers



Hybrid Riser Key Components Flexible jumpers (dynamic bundles) Buoyancy tank (air cans)

Taper joint (or hinge connection)

Core pipe (tether)

Riser bundle (integral/non integral)

Flexjoint (taper joint) Spools (jumpers)


19


Hybrid Riser Towers – Tower Extremity Illustrations Tower-Jumper Interface

Seabed Connection



Single Leg Hybrid Risers

FPSO 50 m Buoyancy Tank (5.0m dia x 25-30m long)

Flexible Jumper

Single Pipe Riser

Riser Base Joint Suction Pile

Flowline


20


.

verv ew o un amen a s o Riser Engineering



Beam Stresses y x z

V y

=

dMz dx

u er- ernou

eam:

Axial stresses much larger than shear stresses

T = σ dA M z

= − ∫ yσ dA


21


Effective Tension 

Global Effects   



Derive effective tension from apparent weight Additional hydrodynamic and mechanical loads add to effective tension Buckling is a function of effective compression (negative effective tension); not true wall compression

Internal Cross-Section Effects   

Work with true wall tension and com ute true wall stress Stress criteria developed from true wall tension and other stresses Von Mises derived from true wall tension EG55F6 Risers Systems and Hydrodynamics


Riser Large Displacements


22


Convected Axes – Deformed Riser



Final Matrix Equations of Motion

 + C d  + K d = F + K d M d − ~

− ~

− ~

~

− ~ r b

= R ~

Mathematically, system of 2nd order linear differential equations Equations are nonlinear as mass and stiffness matrices are functions of displacement. Nonlinear stiffness includes terms that are a function of stress (effective tension) Rigid body terms accounts for large displacement and rotation Solve in Time Domain or Frequency Domain


23


Frequency Domain Method Decompose into 2 equations: Dynamic:

−

−

− ~

~

~

~

K d c = F c + K d rb

Static: Note:

 + C d  + K d = F M d t t t t −

~

−

~

~

M , C and K assumed time-invariant annot app y w ere geometr c non near ty significant in dynamic Note capacity for linearised dynamic about nonlinear static



Frequency Domain Dynamics F t = F 0 ~

e i ω t : d t = d 0 e i ω t : F 0 , d 0

~

~

~

~

− Complex

~

 = − ω 2 d e i ω t d  t = i ω d 0 e i ω t : d t 0 ~

~

~

~

Substitute into dynamic equation ( − ω 2 M + i ω C + K ) d 0 e i ω t = F 0 e i ω t ~

Solve directly for

~

d 0 ~

Solve matrix equation once for single frequency EG55F6 Risers Systems and Hydrodynamics

24


Wave Spectrum Discretisation 

Equal area discretisation Area = S η ( ω n )d ω =

1 2 a n 2

Sη (ω )

ωn

ω, radians/second

dω

N

η (t )

=

∑ a cos( k i =1

i

n

y − ω nt

+ φ i )



Fatigue Calculations: Time Domain vs Frequency Domain 

Spectrum discretised into finite number of harmonics

    



Random wave synthesised by superposition with random phases Generate time-history of wave loading and vessel motions Run time domain analysis for 3 hour storm (54,000 timesteps) Statistical analysis of output timetraces to calculate fatigue damage

Frequency Domain 

Solve equations of motion once for each wave spectrum

 

Generate response spectrum directly Calculate fatigue life from properties of response spectrum


25


Fatigue Calculations Hs (m)

Totals

From

To

0.0024

0.1533

2.1821

10.9055

29.4055

32.5839

14.5441

0

1

0.0024

0.1389

0.4586

1.1013

1.7016

0.5055

0.0934

0.0000

0.0092

0.0000

0.0000

0.0000

4.01104488

1

2

0.0000

0.0140

1.5456

4.9933

12.2997

8.7117

1.6113

0.3840

0.0958

0.0151

0.0048

0.0000

29.6752296

2

3

0.0000

0.0003

0.1732

3.9070

8.5255

11.1960

4.1127

0.9179

0.1215

0.0270

0.0000

0.0000

28.9811682

3

4

0.0000

0.0000

0.0048

0.8611

4.8037

6.5943

3.4991

1.9210

0.3316

0.0441

0.0541

0.0075

18.12123

4

5

0.0000

0.0000

0.0000

0.0376

1.6510

3.0600

2.4005

1.5853

0.5127

0.0376

0.0072

0.0000

9.29179766

5

6

0.0000

0.0000

0.0000

0.0051

0.3539

1.5647

1.3607

1.1369

0.4860

0.0192

0.0096

0.0096

4.94570048

6

7

0.0000

0.0000

0.0000

0.0000

0.0657

0.6708

0.7023

0.6509

0.3919

0.0575

0.0014

0.0000

2.54044251

7

8

0.0000

0.0000

0.0000

0.0000

0.0044

0.2492

0.4908

0.2940

0.0982

0.1109

0.0202

0.0000

8

9

0.0000

0.0000

0.0000

0.0000

0.0000

0.0318

0.2187

0.2361

0.0910

0.0394

0.0007

0.0000

0.61774198

9

10

0.0000

0.0000

0.0000

0.0000

0.0000

0.0000

0.0489

0.1817

0.0554

0.0082

0.0007

0.0000

0.2950103

10

11

0.0000

0.0000

0.0000

0.0000

0.0000

0.0000

0.0055

0.0825

0.0421

0.0072

0.0007

0.0000

0.13792245

11

12

0.0000

0.0000

0.0000

0.0000

0.0000

0.0000

0.0003

0.0284

0.0284

0.0055

0.0007

0.0000

0.06342379

12

13

0.0000

0.0000

0.0000

0.0000

0.0000

0.0000

0.0000

0.0078

0.0165

0.0041

0.0006

0.0001

0.0289774

13

14

0.0000

0.0000

0.0000

0.0000

0.0000

0.0000

0.0000

0.0016

0.0081

0.0027

0.0004

0.0000

0.01292296

14

15

0.0000

0.0000

0.0000

0.0000

0.0000

0.0000

0.0000

0.0002

0.0034

0.0018

0.0003

0.0000

0.00572224

-6.00E+00--5.00E+00

15

16

0.0000

0.0000

0.0000

0.0000

0.0000

0.0000

0.0000

0.0000

0.0013

0.0010

0.0002

0.0000

0.00249835

-7.00E+00--6.00E+00

16

17

0.0000

0.0000

0.0000

0.0000

0.0000

0.0000

0.0000

0.0000

0.0004

0.0006

0.0001

0.0000

0.00107121

-8.00E+00--7.00E+00

17

18

0.0000

0.0000

0.0000

0.0000

0.0000

0.0000

0.0000

0.0000

0.0001

0.0003

0.0001

0.0000

0.00044149

From

0

2

4

6

8

10

12

14

16

18

20

22

2

4

6

8

10

12

14

16

18a g e Dam

20

22

24

1

3

5

7

9

11

13

15

17

19

21

23

Tp (s) To Mean

7.4283

2.2937

0.3821

1.00E-05

1.00E-06

0.1017

0.0173

100

1.26765446

Full-3D Bending

F rom To M ean

1.00E-07

Wave Scatter Diagram 1.00E-08 0 0 - s s 4 3 8 . 6 . 6 6 - m 8 8 3 . 7 . 2 1

Frequency Domain - Solve for each seastate - Fatigue damage from spectrum of response

0 0 - - 5 5 5 s s 4 4 0 1 - - 4 5 0 0 0 s s 6 - 4 . 9 - 9 0 5 . 6 0 s s - 9 5 5 - 9 7 7 s s 5 - 9 - - 3 . 1 - 3 3 5 3 1 s s . 2 . 3 3 m m 7 . 1 3 8 1 - 1 - 6 . 8 - 1 - 6 9 9 . 2 s s - 7 . 3 - 8 m 8 . 0 4 s - 6 . 8 - 8 . 0 m m 7 - 8 0 1 1 2 5 9 m m . 1 . 2 1 5 m m - 9 . 8 . . 8 0 9 2 1 . 6 7 m . 1 4 4 1 1 1 . 8 . 9 . 2 m 2 1 . 3 m m 1 2 3 . 8 9 7 1 7 . . 2 1

5 0 3 0 1 8 8 - 1 s - 1 s s 8 1 0 . 6 7 . 1 0 . 1 1 1 - 1 - 1 m m 2 0 m 8 1 . 9 . 6 1 1 . 1

0 8 1 s 2 6 . 0 1 m 5 3 . 2

0 8 0 0 1 8 8 - 1 s - 1 9 s s 1 1 0 . 3 . 3 1 . 1 2 0 - 1 1 m 1 m m 2 9 . 5 7 . 1 1 . 3 2

0 8 1 s

1 6 . 9 m 5 7 . 1

5 2 2 s

2 6 . 0 1 m 8 6 . 1

5 2 2 s 5 7 . 9 m 5 6 . 1

5 2 2 s 3 8 . 0 1 m 6 1 . 2

Loadcase (Hs1, Tp1, Dir1)

5 2 2 s

9 1 . 0 1 m 9 3 . 2

5 2 2 s

5 2 2 s 9 7 . 1 1 - 1 m 6 m 2 5 . 6 . 3 2 0 9 . 1

315.1 270.1 25.1 180.1 135.1 90.1 45.1 0.1 Location (Wire.Cnr) 5 2 2 s

5 0 . 1 1 m 1 6 . 3

5 2 2 s 7 6 . 0

1 m 3 7 . 2

Fatigue Damage around Cross-Section



Frequency Domain Results (1)

0.01

) m / 1 ( n o i t a i v e D d r a d n a t S e r u t a v r u C

0.008

0.006

0.004

0.002

0 1

2

3

4

5

6

7

8

9

1 0 11 1 2 13 1 4 15 1 6 17 1 8 19 2 0 21 2 2 23 2 4 25 2 6 27 2 8 29 3 0 31 3 2 33 3 4 35 3 6 37

Loadcase No

Curvature at Fatigue Hotpsot EG55F6 Risers Systems and Hydrodynamics

26


Frequency Domain Results (2)

) m / 1 ( n o i t a i

v e D d r a d n a t S e r u t a v r u C

0.0035

0.003

0.0025

0.002

0.0015

0.001

0.0005

0 620

621

622

623

624

625

626

627

628

Distance along riser (m)

Bend Stiffener Region EG55F6 Risers Systems and Hydrodynamics


.

ser

es gn

ons era ons

• • •

Vessel Motions Touchdown Response & Buckling Flexible Pipe Design & Failure Modes

• •

Cross-section impact on global motions Coupled vessel-mooring-riser response EG55F6 Risers Systems and Hydrodynamics

27


Riser Host Vessel Characteristics 1. 2. 3. 4. 5. 6. 7. 8. . 10.

Host Vessel vs Water Depth Host Vessel 6 DoF Motions Vessel Motions & Environmental Forces Mean Loads & Excursions High Frequency Forces & Excursions Low Frequency Motions & Excursions Host Vessel Motion Data for Riser Design Coupled vs Uncoupled Motion Analysis os esse o on arac er s cs Host Motions Induced Riser Fatigue



Types of Mooring Systems


28


Vessel Motions & Environmental Forces • Mean Excursions – Drag dependent •Wind, current

• High Frequency Motions – Heave, Roll & Pitch (buoyancy dominated) – Surge, Sway & Yaw (drag, skin friction dominated) – Not influenced by mooring stiffness or risers

• Low Frequency Motions – Highly mooring stiffness influenced – Interaction of waves of different frequencies in an irregular sea. – Drag dominated



Moored Vessel Motions API Max

LF (sig/max) HF (sig/max) HF (peak)

‘Initial’ Offset for Riser Simulations

Vessel Excursion


29


Vessel 6 DOF Motions



Mean Loads & Excursions 

Constant loads 



Wind & current (6 DOFs, although often only 2 DOFs)

ons ere

n r ser es gn as s a c vesse excurs ons Wind & Current

Static Excursion

Free Hanging Catenary


30


High Frequency Forces & Excursions 1st order, wave frequency component 1.4

Compiled from: Radiation/diffraction programs Generally imposed in riser design as motion RAOs (6 DOFs)

1.2 ) t f / g e d ( O1.0 A R l a n o i t a 0.8 t o R & ) t f / t f ( 0.6 O A R t n e m0.4 e c a l p s i D

0.2

0.0 0

4

8

12

16

20

Period(sec) H eave

S ur ge

24

28

180

Head Sea (incident on Bow)

P ti ch

150 120 ) s e e r g e d (

90 60

t s e r C 30 e v a

W 0 o t 4 t r w -30 s p m A -60 e s a h P

ase Lag

8

12

16

20

24

28

Phase Lead

-90

-120 -150 -180 Period (sec) H ea ve

S ur ge

P ti ch



Low Frequency Motions & Excursions 2nd order wave and wind components (mainly wave) Can be significant loads for severe storms Low damping at these long periods from mooring

Compiled from: Model Tests Radiation/Diffraction analysis

Often imposed in riser design as sinusoidal response superimposed on H F motions


31


Vessel Motion Characteristics TLP Spar Semi FPSO

WF moderate low moderate high

LF low moderate moderate high

Other ringing Hull VIV Hihg heave motions High heave motions



SCR Riser to Host Connection Flex Joints

– – – –

Lower bending to riser porches Lar er confi urations limits HT elastomer performance challenges More expensive than stress joints

Stress Joints

– Current limit: 10” ID, approx 65 ft long (depends on machining and transportation capability) – equ re eng s ong or g mo on vessels – High bending applied to riser porch


32


Flexible Riser to Host Connection Bend Stiffeners Bend Restrictor

Bend Stiffener

Steep Wave



Riser Buckling at Touchdown

PROPOSAL PREPARED FOR

THE OIL COMPANY DATE

n ma on


33


Riser Hang-off Location on FPSO Buckling – Heave & pitch induced heave . – TLP/Spar Vessel: small heave implies riser compression generally not an issue

FPSO: Heave is significant – Pitch induced heave depends on distance from COM – Bow mounted turret is most severe

Sensitivity of Vertical Motion to Riser Hangoff Positioning 2.2 Hangoff 0mForwardof COM

2

Hangoff 50mForward of COM Hangoff 100mForwardof COM

) 1.8 m / m1.6 ( n o1.4 i t o M1.2 l a c 1 i t r e V0.8 f o O0.6 A R0.4

Hangoff 150mForwardof COM Hangoff 200mForwardof COM

0.2 0 0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

Period of Response (s)



Analysis of Post-Buckling Behaviour Beam Element Equations – Use small deformation beam bending equations – Modelling of geometric nonlinearity required to account for post buckling behaviour – Convected Co-ordinates to account for Geometric Nonlinearity under large deformations and DATE rotations

Solution once P cr is not exceeded for each element –

emen eng s s ou

e su c en y sma


34


Riser Hang-off Motions 1.5

) g 1 n i s a e r r e c e t e D0.5 m e a i v r a t P a l g e a N n , 0 o g i s i n 50 n s e a m i e r D c n-0.5 n I o e v N i t i s o P -1 (

55

60

65

70

75

80

85

90

Velocity Acceleration Curvature

-1.5

Time (s)



Non-Dimensional Buckling Parameter V Ter min al

= 2.m.g Cd . ρ . D

drag

PROPOSAL PREPARED FOR

THE OIL COMPANY Drag Force = .Cd.ρ.Ddrag.V2

02.10.02002 Gravitational Force Fd = m.g

Non-Dimensional Buckling Parameter:

π

b

= Vhangoff / Vterminal


35


Curvature vs Non-Dimensional Parameter 4.50

4.00

3.50

e p i P 3.00 / y y t t i i c c o o l l 2.50 e e V V l f a f n o i 2.00 g m n r a e H T x 1.50 a M 1.00 4.5" Water Injeciton Near 6" Production Near

0.50

4.5" Water Injection Far 6" Production Far

0.00 0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

Maximum Resultant Curvature (1/m)

π >1 implies high touchdown curvature b



Tension vs Non-Dimensional Parameter 4.50

4.00

3.50

3.00

/ y y t i t i c c o o l l e e V V f l a f n o i g m n r a e H T x e a i p M P

2.50

2.00

1.50

1.00 .5"Water Inection Near 6" Production Near

0.50

4.5" Water Injection Far 6" Production Far

0.00 -100

-80

-60

-40

-20

0

20

40

60

80

100

Minimum Effective Tension (kN)

Onset of buckling for

π >1 b


36


Flexible Riser Design Issues

Alternative Configurations Free-Hanging Configuration

S Configuration

Wave

Lazy

S

Free Hanging Catenary

Wave Configuration

Lazy Wave

Lazy-S

Steep Pliant Wave® (Tethered)

Steep-S

Steep Wave



Flexible Pipe Cross Section Example : Rough-bore Pipe (with Carcass)

Carcass (Stainless Steel) – External Pressure Resistance Carcass Profile:

Internal Sheath (Polymer) – Internal Fluid Containment Barrier

Pressure Armor (Carbon Steel) – Hoop Load Resistance Armor Profile:

Tensile Armor (Carbon Steel) – Tensile Load Resistance

External Sheath (Polymer) – External Fluid Barrier EG55F6 Risers Systems and Hydrodynamics

37


Flexible Risers: Design Limits Water Depth vs. ID Current Design Limitation: Water Depth vs ID

2500 Field Data Qualification 2000

) m ( 1500 h t p e D r e t a 1000 W

500

0 0

2

4

6

8

10

12

14

16

18

Riser / Flowline ID (in)



Flexible Risers: Design Limits Pressure vs. ID Design Pressure vs ID

DP psi 3" DRAPS 15 000 14 000 13 000 Gyrfalcon Wellstream

12 000

(sweet API17J

P x ID = 90 000

4" Veslefrikk

11 000

P x ID = 67 000

10 000 9 000

9" Aasgard A/B 8 000 7 000 Terra Nova

6 000

Magnus 5000

ro

Vigdis

e s r e am

4 000 Aasgard B

16.6" Aasgard B

3 000 Troll CSO 2 000

Gulfaks Statfjord B

1 000 0 2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

ID in


38


Example Configurations - Animation



Flexible Flexi ble Pipe Bending Bending - Hyst Hysteresi eresis s 

Stick-Slip Bending   

Tensile Armour Armour initially sticks on reverse reverse bending Slip is inline with and transverse to lay-direction Hysteretic fatigue stress 150

100

) a P M 50 ( s s e 0 r t S e -50 r i

Cycle

W

-100

-150 -0 .1

-0.05

0

0.05

0 .1

P i p e D y n a m i c - Cu Cu r v a t u r e ( r a d / m )


39


Hysteresis Curve Cycles 150

100

) a P M 50 ( s s 0 e r t S e -50 r i W -100

-150 -0.1

-0.05

0

0.05

0.1

P ip ip e D y n a m i cc - Cu Cu r v a t u r e ( r a d / m )



Tensile Armour Wire Stress 

Components of stress 



Axial symmetric model

Wire bending stress 

Loxodrom Loxodrome e model model  



Lay angle assumed constrained Wire bends about both principal axes

Friction-induced stress  

Nonlinear hysteretic response The main hurdle to globally integrated stress analysis


40


Wire Equations of Equilibrium d σ 11 ds

t + σ 12,tot = 0

σ 11t κ n

Tangential

− σ 22,diff = 0

2

Surface Normal

1 3

− σ 11t κ t + σ 32,tot = 0

Transverse

Method of Solution



   

ncreme ncrementa nta curvat curvature ure ete eterm rm nes ncreme ncrementa nta non-s non-s p ax a stress Incremental non-slip axial stress determines incremental tangential shear, normal interface and tranverse shear stresses Check Coulomb law and gradually relax stresses while retaining equilibrium Wire curvatures from loxidromic / geodesic equations EG55F6 Risers Systems and Hydrodynamics


Friction-Induced Stress 

MCS Structural Structural Model for Friction Friction – Regular Loading Loading Pipe Bending Curvature

Wire Stress

1.5E-02

80 60

1.0E-02

) m / d 5.0E-03 a r ( e r 0.0E+00 u t a v r -5.0E-03 u C

40

) a P 20 M ( s 0 s e r -20 t S

-40

-1.0E-02

-60

-1.5E-02

-80 0

5

10

15

20

25

30

0

5

10

Time

15

20

25

30

Time

Hysteresis Loop 80 60 ) 40 a P 20 M ( s 0 s e r -20 t S

-40 -60 -80 -1.5E-02 -1.5E-02 -1.0E-02 -1.0E-02 -5.0E-03 0.0E+00 0.0E+00

5.0E-03 5.0E-03

1.0E-02 1.0E-02

1.5E-02 1.5E-02

Pipe Curvature (rad/m)


41


Friction-Induced Stress MCS Structural Model for Friction – Irregular Loading



Pipe Bending Curvature

Wire Stress

0.025 0.02 ) 0.015 s / . d a r 0.005 ( e r 0 u t a -0.005 v r -0.01 u C -0.015 -0.02 -0.025

100 80 60

) a 40 P M 20 ( s s 0 e r t S -20

-40 -60 -80 0

10

20

30

40

50

60

0

10

20

Time (s)

30

40

50

60

Time

Hysteresis Loop 100 80 60 ) a 40 P M ( 20 s s 0 e r t S -20 -40 -60 -80 -0.02

-0.02

-0.01

-0.01

0.00

0.01

0.01

0.02

0.02

Pipe Curvature (rad/m)



3D (out-of-plane) Irregular Seas 3D Pipe Bending in Irregular Seas Hs = 2m, Tp = 13s, 15deg off-bow Global Tension (left) and Curvature (right) Responses 1.70E+06

0.008

0.006

.

0.004 1.60E+06 ) m /

) N ( n o 1.55E+06 i s n e T

0.002 d a

0

r ( e r u t a v r u C

1.50E+06 -0.002

1.45E+06

-0.004

1.40E+06

-0.006 15

35

55

75

95

115

Time (s)

Tension

Local-y Pipe Curvature

Local-z Pipe Curvature


42


3D (out-of-plane) Irregular Seas 3D Pipe Bending in Irregular Seas Hs = 2m, Tp = 13s, 15deg off-bow Armour Total Stress at 8 Equally Spaced Positions on the Cross Section 800E+06

750E+06

700E+06

) 650E+06 a P ( s s e r t S 600E+06

550E+06

500E+06

450E+06 15

35

55

75

95

115

Time (s)

0deg

45deg

90deg

135deg

180deg

225deg

270deg

315deg



Flexible Pipe Failure Modes Outer Sheath Damage



Outer Sheath  

Hole, Tear, Rupture, Crack Ingress of Sea Water

ROV installation of riser repair clamp. Outer sheath was damaged during riser deployment

Repair Clips on riser Section


43


Flexible Pipe Failure Modes 

End Fitting -

      

Tensile armour Pull-out Outer Sheath Pull-out Vent Valve Blockage / Leakage Failure of Sealing System Crack or Rupture of Tensile Armour Structural Failure of End Fitting body or Flange

From OMAE2004-51431, outer sheath failure due to blocked riser vent valve.




Tensile Armour Layers 

Birdcaging or Clustering



Kinking Individual Wire Rupture




44



Carcass   

, , Unlocking Deformation Collapse or Ovalisation



Circumferential Cracking / Wear Fatigue



Pigging Multi-Layer PVDF



Carcass Profile:



SCR Design Issues 

SCR = Steel Catenary Riser


45


Example Systems • Typical for many GOM SCRs • performance with TLPs • Spar low motions favour SCRs

Animation

Animation



SCR Design Process Flowchart Design

Fundamental Stages:

Design Basis i) WD i i) S CR Di am et er iii) Fluids iv) Waves v) Currents vi) Soil vii) TLP Motions

–

–

–

Assumptions

• • • • • • •

Strength (Pipe & FJ) WF Fatigue VIV Fatigue Installation Analysis Interference esgn Fracture Mechanics

• Design Sensitivities • As-Built Design Analysis • Design Verification

Procurement, Construction, Testing

Procurement, Construct & Testing

Installation

Pipe Weights

Pipe

•

Procurement

• • •

F/J Delivery & End Match Fatigue Testing Welding & Spooling

SCFs S-N

Reeled Installation

–

Operation

Installation

Operations

Installation Fatigue

As-installed ROV-surveyed SCR condition


46


SCR Global Configuration • Steel Catenary Riser (SCR) –

– an extension of a seabed pipeline

– Close to 200 SCRs installed or planned – Used for most export risers in GoM – More recently widely employed for production service to semis, Spars, FPSOs and fixed structures. EG55F6 Risers Systems and Hydrodynamics


Key SCR Design Issues 1. Wall-Thickness Design .

-

3. Interference Design 4. Strength Design 5. VIV Design 6. Fatigue Design & Qualification 7. Riser Hangoff (Porch) Design 8. Fracture Mechanics: UT Defect Criteria 9. Installation Engineering EG55F6 Risers Systems and Hydrodynamics

47


Components & Critical Design Areas

Typical hang-off receptacle with flex joint

Taper Stress joint (TSJ)

VIV Strakes Seabed Trenching



SCR Component Design

TSJs and FlexJoints 



TSJs 

Limits curvature without overstress



Transmits bending moment into vessel hang-off



Titanium or Steel Construction

(Courtesy of RTI Energy Services)

FlexJoints 

Combination of steel and elastomer layers



Flexjoint connected to hull via riser porch



Spool connects flexjoint to hull piping



Reduces bending moment at the riser vessel hang-off


48


VIV Suppression: Strakes/Fairings Mitigation of VIV – Under long term and extreme currents

(Courtesy of CRP)

. –

2.

Typically polyurethane, fibreglass or plastic

Fairings –

Typically fibreglass or plastic



Typical SCR Stress Outputs 20-inchGasExport15 degHO 10-inchProduction14degHO 8-inchProduction12degHO

8-inchProduction14degHO

Typical Effective Tension Profile

0 5 7 1 0 0 5 1

) 0 s 5 p 2 i k 1 ( n 0 o 0 i 0 s 1 n e T 0 5 e 7 v i t c e 0 f f 0 5 E 0 5 2

20-inchGas Export 15degHO 10-inchProduction14 degHO 8-inchProduction12 degHO

0

0

2500

5000

7500

10000

Curvilinear Distance along the set SCR(feet)

Typical API RP 2RD Stress Profile

12500

15000

8-inchProduction14 degHO

5 3

) i s 0 k 3 ( s s e r 5 t S 2 s e s i M 0 2 n o v D 5 R 1 2

Touchdown

Hang-Off

P R I 0 P 1 A 5

0

2500

5000

7500

10000

12500

15000

Curvilinear Distance along the set SCR(feet)


49


Fatigue Life Along SCR Length 1,000,000,000

100,000,000 , ,

10,000,000 ) s r a e y ( e f i L e u g i t a F

1,000,000

Dirliks Rayleigh

100,000

Han -Off

10,000 ,

Seabed Touchdown

1,000

100 0

500

1000

1500

2000

2500

3000

3500

4000

4500

Distance from Top of SCR (ft)



SCR Touchdown Fatigue 

Behaviour at SCR touchdown oint (TDP) key design driver 



Fatigue

TDP response source of design uncertainty  

Soil properties Limitations of soil models EG55F6 Risers Systems and Hydrodynamics

50


SCR-Soil Interaction Modelling 

Non-linear soil modelling now included in Flexcom



STRIDE JIP 

Soil suction model using soil force-deflection curve



CP Anodes, Inhibitors & Coatings 1. External Corrosion Protection •

Determine required anode mass and spacing

2. External Corrosion Coatings • • •

FBE corrosion protection mechanically bonds pipe materials to external insulation (PE, PP) Typically TLPE for TDP Often TSA for straked sections

3. Corrosion Inhibitors •

Corrosion protection/inhibition within SCR.


51


Insulation / Heating Technology State of the Art 





Passive approach using the thermal inertia of materials added around the element to insulate. Important properties of the materials are: 

Thermal conductivity



Heat capacity



Density

Active approach by adding some thermal energy to maintain the element at a given temperature. Energy can be brought by: 

Hot water



Electricity  Direct heating  Skin effect  Induction

Mixed approach combining the two technical solutions described above



Riser Concepts – Flow Assurance 1.

SCR / Riser Tower 

With or without wet insulation



Improved Flow Assurance Significantly heavier

.

- 

3.

Flexible Pipe w/ insulation 

4.

Integrated Production Bundle (IPB)  

5.

Proven design & track record

Integrated Gas Lift, heating and services Evolving technology – based on flexible pipe

Integrated Production Umbilical (IPU)  

Integrated Gas Lift, heating and services Evolving technology – based on SCR


52


Riser Concepts (continued) 6.

Single Leg Hybrid Riser (SLHR) – Single Pipe  

7.

Single Leg Hybrid Riser (SLHR) – Pipe-in-Pipe 

8.

Dry insulation

Hybrid Bundle Riser (SLHR) 

9.

With or without wet insulation Combines steel and flexible pipe

Wet insulated bundle

Top Tensioned Riser (TTR)



Integrated Production Bundle (1) External Plastic Sheath Thermal Insulation Tubes for Hot Water or/and Gas Lift

Flexible Riser Structure Technip Patent


53


Integrated Production Bundle (2)

Courtesy Technip



Riser Solutions – Flow Assurance


54


Integrating Riser Design & Flow Assurance 

Key items of integration 

Insulation and its impact on riser drag-to-weight ratio fatigue damage



Deep Water Steel Catenary Riser Example  



Methodology of Investigation  



How does riser shape influence slugging? How does slugging affect fatigue life? Perform slugging analysis with multiphase transient flow assurance software Link flow assurance output with riser dynamics software and compute response

Key Findings 

Slugging can have significant fatigue damage and depends of type of slugging and inclination of flowline into riser EG55F6 Risers Systems and Hydrodynamics


Flow Assurance & Riser Dynamics 

Riser Insulation: 



Drag-to-weight Ratio    



Drag is a destabilising horizontal force and is proportional to riser diameter Weight (in water) is a vertically downward stabilising force Drag-to-weight (DTW) ratio is a measure of hydrodynamic stability Riser values vary from 2m2 /tonf to 8 m2 /tonf

Insulation increases the DTW value 



Increases outside diameter of pipe at lower density levels

Limit on amounts of insulation for catenary risers

Effective Tension is important for buoyant and top tensioned risers EG55F6 Risers Systems and Hydrodynamics

55


Flow Assurance & Riser Dynamics 

Riser Slugging:  



Impact of riser slugging on riser fatigue

Force terms from:   

changes in pressure and density centripetal due to slug velocity along curved coriolis due to fluid motion in the moving riser frame of reference



Slugging Characterisation WADO - Slugging Example - PPL Data 10" Flowline, Downslope, 20000 BPD, 90% Water Cut, 150 Sm3/Sm3 Slug Length Profiles (4x) 800 1.00 hours 1.25 hours

700

1.50 hours 1.75 hours 2.00 hours

600

2.25 hours 2.50 hours

500

2.75 hours 3.00 hours

400

300

200

100

0 15000

16000

17000

18000

19000

20000

21000

22000

23000

24000

25000

26000

27000

28000

Distance (feet)

Time, length and location of slugs EG55F6 Risers Systems and Hydrodynamics

56


Riser Model Discretisation SLUG

15 m Sect 1

15 m Sect 2

Riser discretisation for slug force computation

15 m Sect 3

WADO - SCR Touchdown Point Fatigue Enhancements 10" Catenary Riser Profile 0

Riser section identification

TOPSIDES -250

RISER_2C RISER_2 RISER_3 RISER_3

-500

RISER_3

-750

RISER_1C RISER_1A

RISER_3

RISER_1D RISER_1B

Force terms computed from fluid pressure and density , coriolis forces due to slug / riser motions

RISER_2D RISER_2B -1000 -1250 -1500 -1750 -2000 -2250 -2500 0

250

500

750

1000

1250

1500

1750

2000

2250

Distance from FPSO, m



Coupled vs Uncoupled Motions •Coupled Motion Analysis (Hydrodynamic coupling) •(QTFs, wave forces RAOs, current & wind force coefficients, radiation damping &

added matrices) •Re uired if inertia dam in response of host facility

stiffness of risers & moorin si nificantl affect

•Uncoupled •RAOs, offsets, sinusoidal drift •Full vessel time history (Spar generally)

Prescribed Motions


57


Installation Vessels - SCRs

J-Lay

Reel Lay



Installation, Schedule, Cost Drivers

Steel Riser and Flowline  S-lay Installation 





J-lay 



used up to moderately deep water, modified stinger for very deep water limit is curvature induced at stinger deep to ultra-deep water riser installation, typically expensive option

Reel-lay Faster than J-Lay with more controlled shop (2G - horiz) instead of offshore (5G) welding  More complex weld testing and fracture mechanics – Large diameter may imply high reeling strains – max strain and low cycle fatigue challenges – Requires nearby spool base to be economical (WoA challenge) 


58


Riser & Flowline System Selection

Impact on Cost and Schedule 

Flexible Pipe – Tradeoff = procurement cost vs. installation cost



Steel Flowlines and SCRs – Often lowest procurement cost in deepwater – Deepwater pipelay vessel : J-Lay or reeled lay typical for deepwater applications, S-Lay for shallow-moderate depth



Riser Towers – Typically most expensive riser installation option – un e ns a a on yp ca y y ow-ou – SLHR installation may be pipelay vessel or MODU installation



Installation Challenges and Vessel Capacity ●

Installation Challenges      

●

Ultra-deepwater high tension loads Lar e diameter Positioning for TDP & clashing during transfer Rigging/handling of pull-in/abandonment Weather fatigue during installation Vessel on-site vs. abandonment & recovery (A&R)

Installation Vessel Capacities: ompany

esse

Lay tension (kips)

ay ype

Max. Pipe Size (in)

Heerema

Balder

2800

J

30

Technip

Deep Blue

1697

R, J

28

Global

Hercules

1200

S, R

60 (S), 18 (R)

Saipem

S-7000

1160

J

32

Allseas

Solitaire

2,500

S

60

Based on Reported Tension Capacities (2003)


59


Procurement & Installation Costs 

Procurement Costs – – – – –





Line Pipe or flexible pipe Corrosion Protection coatin s Insulation Coating (riser/flowline), concrete coating (flowline) J-lay Collars Ancillary devices (Flexjoints, strakes, anodes, buoys, clamps, bases, bend stiffeners/restrictors, buoyancy modules/tanks, pipe supports or mudmats)

Installation Cost – Mobilization – Prefabrication (onboard or at spool base) – Offshore Installation = f (vessel, inst. method) – Lifting and handing over to receptacle – Tie-in & hydrotest – Demobilization Miscellaneous – Engineering, Inspection, Contingency



Issues Considered 

Riser Types 

TTRs, Flexibles, SCRs, Hybrids

ser un amenta s

   

Tension / Bending, Effective Tension Large displacements Time Domain vs Frequency Domain 



Vessel motions 

   

Extreme vs Fatigue Touchdown buckling

Thermal considerations Riser Design and Flow Assurance Drag-to-Weight Ratio Installation EG55F6 Risers Systems and Hydrodynamics

60

Riser Overview Lecture Feb 2011

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