riser overview lecture feb 2011

1

MSc in Subsea Engineering

EG55F6 Risers Systems and Hydrodynamics

Overview of Riser EngineeringDr Patrick O’BrienHonorary Professor of Engineering, University of Aberdeen & Group Director, MCS Kenny


Presentation Overview

1. General Concepts & Field Layout

2. Riser System Types

3. Overview of Fundamentals of Riser Engineering

4. Riser Design Considerations


2


Key Messages

Dry tree vs wet tree: Tensioned vs Compliant

Riser TypesypTTRs, Flexibles, SCRs, Hybrids

Riser FundamentalsLarge displacement, effective tension, equations of motion, time vsfrequency domain

Riser Design ConsiderationsVessel motionsTouchdown response and buckling


Touchdown response and bucklingFlexible pipe design issues and failure modesSCR design issues: touchdown and top connection flex/stress jointInternal flow regime and insulationCross-section impact on global motionsCoupled vessel-mooring-riser response


1 G l C t & Fi ld L t1. General Concepts & Field Layout

• Dry Tree vs Wet Tree• Tensioned vs Compliant


3


RESERVOIR CONDITIONS

ENVIRONMENTAL

Riser System Selection

FIELD LAYOUT

SURFACE UNIT

PRODUCTION SCHEME

CONDITIONS


RISERSYSTEM


System Architecture: Girassol Subsea


4


Boomvang Nansen Fields



Two Main Riser Types“Dry Tree” riser“Wet Tree” riser

Preliminaries:(Christmas) Tree ~ “manifold” type structure


( ) ypPoint at which reservoir fluid iscontrolled“Head” of the well

Tree at seabed ~ “Wet” TreeTree at sea surface ~ “Dry” Tree

5


Feasibility of Dry or Wet Tree...

“A riser should be vertical below wellhead (or Tree)”Tree)

to allow equipment to be transmitted through the well

If Dry tree riser...Riser must be vertical (from surface to seabed)Cannot be connected directly to moving vessel


Cannot be connected directly to moving vesselIf Wet tree riser...

No need to be vertical (from surface to seabed)Can connect directly to vessel (Slack in Riser)


Dry vs Wet Tree Fundamentals

How to cope with motions of vessel (Dry)Riser Supported Vertically by buoyancy canspp y y y yRiser connected to vessel by Tensioners

Tensioners (like springs) extend and compressRiser top response decoupled from vessel motions

Vessel Heaves, riser doesn’t

How to cope with motions of vessel (Wet)


( )Riser connected directly to vesselEnough slack/compliancy built into riser

e.g. use of Wave shape configuration

6


Offshore Production Facility Types



Floating Production Vessel Types

FPSO

SemiD d ft

Mini TLP


Deep draft

SPAR

7


Independence Hub Semi

World’s deepest risers…2,438m

SCRs – 7 Initial- 9 Future

Umbilicals


Umbilicals –STU


Technology Limits: Water Depth

Deepest Semisubmersible (Independence Hub approx 2,440m)( p pp )(Nakika 1,920m)

Deepest TLP (Magnolia approx 1,433m)


Deepest Spar (Devil’s Tower approx 1,707m)

8


2 Ri S t T2. Riser System Types

• Top Tensioned Risers (TTRs)• Flexible Risers• Steel Catenary Risers (SCRs)• Hybrid Steel Flexible Risers


• Hybrid Steel-Flexible Risers


SPAR Top Tensioned Risers


9


SPAR Risers - Detail



Riser Top Tensioners (TLP)


10


Individual Riser Tensioners



Top Tension Riser Design


11


Dry vs Wet Tree Design

• Must have dual independent barrier between uncontrolled reservoir fluid and environment

Outer Annulus

Inner Annulus

13 3/8 “ Outer Casing

9 5/8” Inner Casing

5 ½” Production Tubing

– I.e. below wellhead

• Dry Tree– Single or Dual Casing Riser

• (from Seabed to Surface)


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


TTR Riser Design Issues

What is the wall thickness of casings?Withstand stresses (hoop axial bending )Withstand stresses (hoop, axial, bending,..)Extreme, fatigue, VIV loading

How many cans/tensioners required to support the risers?


Tapered sections (reinforcements at seabed and vessel interfaces)

12


Flexible Risers



Flexible Pipe Cross SectionCarcass (Stainless Steel)

– External Pressure Resistance

Carcass Profile:

Example : Rough-bore Pipe (with Carcass)

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

13


FREE HANGING LAZY WAVE STEEP WAVE

Flexible Riser Configurations


PLIANT WAVE® STEEP S LAZY S


Bend Stiffeners

FunctionPrevents over-bending Bend

Stiffener

Provides moment transition between flexible and rigid end connection

Design ConsiderationsPolyurethane fatigue and creep

Non-linear material propertiesSteel collar for load transfer

Steep Wave


Steel collar for load transferInterface arrangement

e.g. I-tubes, porch,Manufacturing tolerances

14


Buoyancy Devices

TypesDistributed – lazy wave and steep wave configurations

Configuration achieved by buoyancy modulesManufacturers include

Trelleborg CRP LtdFlotechEmerson Cuming

Concentrated – lazy S and steep S configurationsConfiguration achieved by tether buoy


g y yManufacturers include

Trelleborg CRP Ltd


Distributed BuoyancyDistributed

Steep-waveLazy wave Lazy PliantSteepLazy-wavePliant waveFloatation attached to result in desired riser configurationBuoyancy Supplied by discrete modules

Lazy Wave

Pliant Wave®

Steep Wave


Clamps required for buoyancy module to make connection to pipe

15


Distributed Buoyancy

Design considerations– Usually syntactic foam– Net buoyancy requirement

output from configuration design– Clamping


gModule slippage can alter

configuration– Gradual loss of buoyancy over time– Clashing


Distributed Buoyancy

Buoyancy Module2 half shellsHeld in place by clampHalf shells strapped together over clampProfiled to avoid overbending of riser


overbending of riser

16


Distributed Buoyancy Issues• Numerical modeling of modules -

discrete or smeared• Accounting for parameters that reduce g p

buoyancy:– Water absorption– Initial elastic compression– Creep– Marine growth– Manufacturing tolerances

• Review of design requirements for system with lost modules currently

Courtesy of Trelleborg CRP Ltd.


system with lost modules - currently 10% in API RP 17B

• Guidance on module spacing


Concentrated BuoyancyConcentrated buoyancy

Steep-SLazy-Sy S

Design considerationsUsually pressurized steel tanksBuoyancy requirement

ensure taut in all internal fluid conditionsCompartmentalized buoyancy tanks

Steep-S Lazy-S


RedundancyTether hold-down arrangementGutter to prevent interference

17


Subsea Arch



Subsea Arch


18


Subsea Arches - Key Issues

• Redundancy for mid-water arches with buoyancy tanks in case of fl d d t k/ t tflooded tank/compartment– Depends on risk level i.e. production

(oil) versus water service over mid-water arch

– Too much redundancy can be prohibitive

– Tolerances– Arch Sizing – Installation issues


gCourtesy of Trelleborg CRP Ltd.


Steel Catenary Risers


19


Steel Catenary Risers



Hybrid Riser Key Components

Flexible jumpers(dynamic bundles)

Buoyancy tank(air cans)

Taper joint (or hinge connection)

Riser bundle (integral/non integral)Core pipe

(tether)


Spools (jumpers)

Flexjoint (taper joint)

20


Hybrid Riser Towers – Tower Extremity Illustrations

Tower-Jumper Interface

Seabed Connection



Single Leg Hybrid Risers

Bend StiffenerFPSO

Single Pipe Riser

Bend StiffenerFPSO

FlexibleJumper

Rigid Jumper

50 mBuoyancy Tank (5.0m diax 25-30m long)

Riser Base Joint


Rigid Jumper

FlowlineSuction Pile

21


3 O i f F d t l f3. Overview of Fundamentals ofRiser Engineering



Beam Stressesy

x

∫= dAT σ

z

dxdMzVy =

E l B lli B


∫

∫−= dAyM z σAxial stresses much larger than shearstresses

Euler-Bernoulli Beam:

22


Effective Tension

Global EffectsDerive effective tension from apparent weightAdditional hydrodynamic and mechanical loads add to effective tensionBuckling is a function of effective compression (negative effective tension); not true wall compression

Internal Cross-Section EffectsWork with true wall tension and compute true wall


pstressStress criteria developed from true wall tension and other stressesVon Mises derived from true wall tension


Riser Large Displacements


23


Convected Axes – Deformed Riser



RdKFdKdCdM =+=++

Final Matrix Equations of Motion

~rb~~~~~ −−−−

Mathematically, system of 2nd order linear differential equationsEquations 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

24


Frequency Domain MethodDecompose into 2 equations:

dddDynamic:

Static:

~t

~t

~t

~t FdKdCdM =++

−−−

~rb

~c

~c dKFdK

−−+=

Note: M, C and K assumed time-invariantC t l h t i li it


Cannot apply where geometric nonlinearity significant in dynamicNote capacity for linearised dynamic aboutnonlinear static


Frequency Domain Dynamics

~~

ti

~~t

ti

~~t Complexd,F:edd:eFF ωω

0000 −==

Substitute into dynamic equation

ti

~~t

ti

~~t edd:edid ωω ωω 0

20 −==

ti

~

ti

~eFed)KCiM( ωωωω 00

2 =++−


Solve directly for d0~

Solve matrix equation once for single frequency

25


Wave Spectrum Discretisation

Equal area discretisationArea =Sη(ω n )dω = 1

2 a2n

ωn

Sη(ω )

ω, radians/second

Area =Sη(ω n )dω = 12 a2nArea =Sη(ω n )dω = 12 a2n

ωnωn

Sη(ω )Sη(ω )

ω, radians/second


dω

,

dωdω

,

η ω φ( ) cos( )t a k y ti ni

N

n i= − +=∑

1


Fatigue Calculations: Time Domain vs Frequency Domain

Spectrum discretised into finite number of harmonics

Time DomainTime DomainRandom wave synthesised by superposition with random phasesGenerate time-history of wave loading and vessel motionsRun time domain analysis for 3 hour storm (54,000 timesteps)Statistical analysis of output timetraces to calculate fatigue damage

Frequency DomainSolve equations of motion once for each wave spectrum harmonic (50 harmonics)


harmonic (50 harmonics)Generate response spectrum directlyCalculate fatigue life from properties of response spectrum

26


Fatigue CalculationsFrom To 0.0024 0.1533 2.1821 10.9055 29.4055 32.5839 14.5441 7.4283 2.2937 0.3821 0.1017 0.0173 100

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 4.011044881 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 29.67522962 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 28.98116823 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 18.121234 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 9.291797665 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 4.945700486 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

Hs (m) Totals

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 1.267654468 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 0.617741989 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 0.1379224511 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 0.0634237912 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 0.028977413 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 0.0129229614 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 0.0057222415 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 0.0024983516 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 0.0010712117 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 FromTo 2 4 6 8 10 12 14 16 18 20 22 24 ToMean 1 3 5 7 9 11 13 15 17 19 21 23 Mean

Tp (s)

Wave Scatter Diagram

225.1270.1

315.1

m-6

.84

s-0

m-6

.63

s-0

m-5

.60

s-0

-5.9

1s-

0.3

6s-

45

10

s-4

5

27

s-4

5

7s-

45

3s-

90

s-9

0

s-9

0

-90

35

35 5 5

1.00E-08

1.00E-07

1.00E-06

1.00E-05

Damage

Full-3D Bending

-6.00E+00--5.00E+00

-7.00E+00--6.00E+00

-8.00E+00--7.00E+00


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

of response

0.145.1

90.1135.1

180.1225.1

2.3

8m

1.7

8m

1.8

9m

1.8

9m

-2

.20

m-7

1.8

5m

-6.

1.8

9m

-6.2

1.6

1m

-7.3

2.1

5m

-8.1

3

1.8

7m

-6.8

1

1.9

4m

-8.2

3s

2.2

4m

-8.3

8s-

1.3

3m

-9.0

0s-

1

1.7

8m

-10

.14

s-1

3

2.7

9m

-9.2

7s-

13

1.8

2m

-10

.08

s-1

35

1.9

0m

-11

.61

s-1

80

1.6

1m

-11

.17

s-1

80

2.3

5m

-10

.62

s-1

80

1.9

1m

-11

.19

s-1

80

3.5

2m

-12

.31

s-1

80

2.1

7m

-10

.30

s-1

80

1.7

5m

-9.6

1s-

18

0

1.6

8m

-10

.62

s-2

25

1.6

5m

-9.7

5s-

22

5

2.1

6m

-10

.83

s-2

25

2.3

9m

-10

.19

s-2

25

3.5

6m

-11

.90

s-2

25

2.6

2m

-11

.79

s-2

25

3.6

1m

-11

.05

s-2

25

2.7

3m

-10

.67

s-2

25

Location (Wire.Cnr)

Loadcase (Hs1, Tp1, Dir1)

Fatigue Damagearound Cross-Section


Frequency Domain Results (1)

0.004

0.006

0.008

0.01

Curvature Stand

ard De

viation (1/m

)


0

0.002

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37

Loadcase No

Curvature at Fatigue Hotpsot

27


Frequency Domain Results (2)

0.001

0.0015

0.002

0.0025

0.003

0.0035

Curvature Standard Deviatio

n (1/m

)


0

0.0005

620 621 622 623 624 625 626 627 628

Distance along riser (m)

Bend Stiffener Region


4 Ri D i C id ti4. Riser Design Considerations

• Vessel Motions• Touchdown Response & Buckling• Flexible Pipe Design & Failure Modes• Internal Flow Regime and Insulation


• Internal Flow Regime and Insulation• Cross-section impact on global motions• Coupled vessel-mooring-riser response

28


Riser Host Vessel Characteristics

1. Host Vessel vs Water Depth2. Host Vessel 6 DoF Motions3. Vessel Motions & Environmental Forces4. Mean Loads & Excursions5. High Frequency Forces & Excursions6. Low Frequency Motions & Excursions7. Host Vessel Motion Data for Riser Design8. Coupled vs Uncoupled Motion Analysis9 H t V l M ti Ch t i ti


9. Host Vessel Motion Characteristics10. Host Motions Induced Riser Fatigue


Types of Mooring Systems


29


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


g y g– Interaction of waves of different frequencies in

an irregular sea.– Drag dominated


Moored Vessel Motions

API MaxMean

HF (peak)

Mean LF (sig/max)HF (sig/max)

‘Initial’ Offset for Riser Simulations


Vessel Excursion

30


Vessel 6 DOF Motions



Mean Loads & ExcursionsConstant loads

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

Considered in riser design as static essel e c rsionsConsidered in riser design as static vessel excursions

Wind & Current

Static Excursion


Free Hanging Catenary

31


High Frequency Forces & Excursions

1st order, wave frequency component

Compiled from:Model tests

1.2

1.4

deg/

ft)

Model testsRadiation/diffraction

programsGenerally imposed in riser

design as motion RAOs (6 DOFs)

0.0

0.2

0.4

0.6

0.8

1.0

0 4 8 12 16 20 24 28

Period (sec)

Dis

plac

emen

t RA

O (f

t/ft)

& R

otat

iona

l RA

O (

Heave Surge Pitch

60

90

120

150

180

(deg

rees

)

Ph

Head Sea (incident on Bow)


-180

-150

-120

-90

-60

-30

0

30

4 8 12 16 20 24 28

Period (sec)

Phas

e A

mps

wrt

to W

ave

Cre

st (

Heave Surge Pitch

PhaseLead

PhaseLag


Low Frequency Motions & Excursions

2nd order wave and wind components (mainly wave)Can be significant loads for severe stormsLow damping at these long periods from mooring

Compiled from:Model TestsRadiation/Diffraction analysis

Often imposed in riser design as sinusoidal response superimposed on HF motions


32


Vessel Motion Characteristics

WF LF OtherTLP moderate low ringingg gSpar low moderate Hull VIVSemi moderate moderate Hihg heave motionsFPSO high high High heave motions



SCR Riser to Host Connection

Flex Joints– Lower bending to riser porches– Larger configurations limitsLarger configurations 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)R i d l th i l f hi h ti


– Required length is long for high motion vessels

– High bending applied to riser porch

33


Flexible Riser to Host ConnectionBend StiffenersBend Restrictor


Steep WaveSteep Wave

Bend Stiffener


Riser Buckling at Touchdown

THE OIL COMPANYPROPOSAL PREPARED FOR

A i ti

DATE


Animation

34


Riser Hang-off Location on FPSO

Buckling– Heave & pitch induced heave

dominated

Sensitivity of Vertical Motion to Riser Hangoff Positioning

2

2.2Hangoff 0m Forward of COMHangoff 50m Forward of COMHangoff 100m Forward of COMdominated.

– 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 0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

RA

O o

f Ver

tical

Mot

ion

(m/m

) Hangoff 150m Forward of COMHangoff 200m Forward of COM


severe 00 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

DATE

– Modelling of geometric nonlinearity required to account for post buckling behaviour

– Convected Co-ordinates to account for Geometric Nonlinearity under large deformations and rotations

Solution once Pcr is not exceeded for each element

Element lengths sho ld be s fficientl small


– Element lengths should be sufficiently small

35


Riser Hang-off Motions

1.5

-0.5

0

0.5

1

50 55 60 65 70 75 80 85 90

Non

Dim

ensi

onal

Par

amet

erve

Incr

easi

ng, N

egat

ive

Dec

reas

ing )


-1.5

-1

Time (s)

N (

Posi

tiv

VelocityAccelerationCurvature


Non-Dimensional Buckling Parameter

PROPOSAL PREPARED FOR

dragalTer DCd

gmV ....2

min ρ=

THE OIL COMPANY

02.10.02002

Drag Force

= .Cd.ρ.Ddrag.V2

Drag Force

= .Cd.ρ.Ddrag.V2


Gravitational Force

Fd = m.g

Gravitational Force

Fd = m.g

Non-Dimensional Buckling Parameter: πb = Vhangoff / Vterminal

36


Curvature vs Non-Dimensional Parameter

3.50

4.00

4.50

0.50

1.00

1.50

2.00

2.50

3.00

Max

Han

goff

Velo

city

/Pip

eTe

rmin

al V

eloc

ity

4.5" Water Injeciton Near6" Production Near 4.5" Water Injection Far


0.000 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8

Maximum Resultant Curvature (1/m)

6" Production Far

πb>1 implies high touchdown curvature


Tension vs Non-Dimensional Parameter

4.00

4.50

1.00

1.50

2.00

2.50

3.00

3.50

Max

Han

goff

Velo

city

/Pi

pe T

erm

inal

Vel

ocity

4.5" Water Injection Near


0.00

0.50

-100 -80 -60 -40 -20 0 20 40 60 80 100

Minimum Effective Tension (kN)

4.5 Water Injection Near6" Production Near4.5" Water Injection Far6" Production Far

Onset of buckling for πb>1

37

MSc in Subsea EngineeringFlexible Riser Design Issues

Alternative ConfigurationsS

ConfigurationWave

ConfigurationFree-HangingConfiguration

Free Hanging Catenary

Lazy WaveLazy-S

LazySWave


Pliant Wave®(Tethered)

Steep-S Steep Wave

Steep


Flexible Pipe Cross SectionCarcass (Stainless Steel)

– External Pressure Resistance

Carcass Profile:

Example : Rough-bore Pipe (with Carcass)

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

38


Current Design Limitation: Water Depth vs ID

Water Depth vs. IDFlexible Risers: Design Limits

1000

1500

2000

2500

Wat

er D

epth

( m

)

Field Data

Qualification


0

500

0 2 4 6 8 10 12 14 16 18

Riser / Flowline ID (in)


Design Pressure vs ID

15 000

DP psi3" DRAPS

Pressure vs. IDFlexible Risers: Design Limits

5 000

6 000

7 000

8 000

9 000

10 000

11 000

12 000

13 000

14 000

4" Veslefrikk

9" Aasgard A/B

Terra Nova

MagnusT ll W ll t

Gyrfalcon Wellstream

(sweet API17J P x ID = 90 000

P x ID = 67 000


0

1 000

2 000

3 000

4 000

5 000

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20ID in

16.6" Aasgard B

Troll CSOGulfaks

Vigdis

Statfjord B

Aasgard B

Troll Wellstream

39


Example Configurations - Animation



Flexible Pipe Bending - Hysteresis

Stick-Slip BendingTensile Armour initially sticks on reverse bendingSlip is inline with and transverse to lay-directionHysteretic fatigue stress

Regular Stress0

50

100

150

ress

(M

Pa)


Regular Stress Cycle

-150

-100

-50

-0.1 -0.05 0 0.05 0.1

Pipe Dynamic-Curvature (rad/m)

Wir

e S

tr

40


Hysteresis Curve Cycles

150

-50

0

50

100

Wir

e S

tres

s (M

Pa)


-150

-100

-0.1 -0.05 0 0.05 0.1

Pipe Dynamic-Curvature (rad/m)


Tensile Armour Wire Stress

Components of stressTension inducedTension-induced

Axial symmetric model

Wire bending stressLoxodrome model

Lay angle assumed constrainedWire bends about both principal axes


Friction-induced stressNonlinear hysteretic responseThe main hurdle to globally integrated stress analysis

41


Wire Equations of Equilibrium

0,1211 =+ tott

dsd σσ

Tangential 2

Method of SolutionI t l t d t i i t l li i l t

0,2211 =− diffnt σκσ

0,3211 =+− tottt σκσ

Surface Normal

Transverse

13


Incremental curvature determines incremental non-slip axial stressIncremental non-slip axial stress determines incremental tangential shear, normal interface and tranverse shear stressesCheck Coulomb law and gradually relax stresses while retaining equilibriumWire curvatures from loxidromic / geodesic equations


Friction-Induced StressMCS Structural Model for Friction – Regular Loading

Pipe Bending Curvature

1.0E-02

1.5E-02

/m)

Wire Stress

40

60

80

)

-1.5E-02

-1.0E-02

-5.0E-03

0.0E+00

5.0E-03

0 5 10 15 20 25 30

Time

Cur

vatu

re (r

ad/

-80

-60

-40

-20

0

20

0 5 10 15 20 25 30

Time

Stre

ss (M

Pa)

Hysteresis Loop

40

60

80

a)


-80

-60

-40

-20

0

20

-1.5E-02 -1.0E-02 -5.0E-03 0.0E+00 5.0E-03 1.0E-02 1.5E-02

Pipe Curvature (rad/m)

Stre

ss (M

Pa

42


Friction-Induced StressMCS Structural Model for Friction – Irregular Loading

Wire Stress

6080

100

)

Pipe Bending Curvature

0 010.0150.02

0.025

d/s)

-80-60-40-20

02040

0 10 20 30 40 50 60

Time

Stre

ss (M

Pa)

-0.025-0.02

-0.015-0.01

-0.0050

0.0050.01

0 10 20 30 40 50 60

Time (s)

Cur

vatu

re (r

ad

Hysteresis Loop

6080

100

)


-80-60-40-20

02040

-0.02 -0.02 -0.01 -0.01 0.00 0.01 0.01 0.02 0.02

Pipe Curvature (rad/m)

Stre

ss (M

Pa)


3D (out-of-plane) Irregular Seas3D Pipe Bending in Irregular SeasHs = 2m, Tp = 13s, 15deg off-bow

Global Tension (left) and Curvature (right) Responses

1 65E+06

1.70E+06

0.006

0.008

1 45E 06

1.50E+06

1.55E+06

1.60E+06

1.65E+06

Tens

ion

(N)

-0.002

0

0.002

0.004

Cur

vatu

re (r

ad/m

)


1.40E+06

1.45E+06

15 35 55 75 95 115Time (s)

-0.006

-0.004

Tension Local-y Pipe Curvature Local-z Pipe Curvature

43


3D (out-of-plane) Irregular Seas3D Pipe Bending in Irregular SeasHs = 2m, Tp = 13s, 15deg off-bow

Armour Total Stress at 8 Equally Spaced Positions on the Cross Section800E+06

550E+06

600E+06

650E+06

700E+06

750E+06

Stre

ss (P

a)


450E+06

500E+06

15 35 55 75 95 115Time (s)

0deg 45deg 90deg 135deg 180deg 225deg 270deg 315deg


Flexible Pipe Failure Modes

Outer SheathHole, Tear, Rupture, Crack

Outer Sheath Damage

Ingress of Sea Water

Repair Clips on riser Section

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


44



End FittingInternal Pressure Sheath Pull-outInternal Pressure Sheath Pull outTensile armour Pull-outOuter Sheath Pull-outVent Valve Blockage / LeakageFailure of Sealing SystemCrack or Rupture of Tensile


ArmourStructural Failure of End Fittingbody or Flange From OMAE2004-51431, outer

sheath failure due to blocked riser vent valve.



Tensile Armour LayersMultiple Wire RuptureMultiple Wire RuptureBirdcaging or ClusteringKinkingIndividual Wire Rupture


45



Carcass Hole Crevice Pitting or ThinningHole, Crevice, Pitting or ThinningUnlocking DeformationCollapse or OvalisationCircumferentialCracking / Wear Fatigue

Carcass Profile:


PiggingMulti-Layer PVDF


SCR Design Issues

SCR = Steel Catenary Riser


46


Example Systems

• Typical for many GOM SCRs

• FavourableFavourable performance with TLPs

• Spar low motions favour SCRs


AnimationAnimation


SCR Design Process Flowchart

Fundamental Stages:

Design

• Strength (Pipe & FJ) • WF Fatigue • VIV Fatigue • Installation Analysis • Interference

CP D i

Assumptions

Design Basis i) WD ii) SCR Diameter

Design

– Design

– Procurement, Construction, Testing

– Installation

• CP Design • Fracture Mechanics

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

Procurement, Construct & Testing

• Procurement • Delivery & End Match • Fatigue Testing • Welding & Spooling

Pipe

F/J

S - N

SCFs

Pipe Weights

)iii) Fluids iv) Waves v) Currents vi) Soil vii) TLP Motions

Reeled


– Operation Installation

Operations

As-installed ROV-surveyed SCR condition

Installation

Installation Fatigue

47


SCR Global Configuration

• Steel Catenary Riser (SCR)Simple catenary shape effectively– Simple catenary shape – effectively 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.


Key SCR Design Issues

1. Wall-Thickness Design

2 Host Vessel Layout and tie-in2. Host Vessel Layout and tie in

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

48


Components & Critical Design Areas

Typical hang-off receptacle with flex joint

Taper Stress joint (TSJ)


VIV StrakesSeabed Trenching

MSc in Subsea EngineeringSCR Component Design

TSJs and FlexJointsTSJs

Limits curvature without overstress

Transmits bending moment into vessel hang-off

Titanium or Steel Construction

FlexJointsCombination of steel and elastomer layers

Flexjoint connected to hull via riser porch

Bellows may be required

(Courtesy of RTI Energy Services)


Bellows may be required

Spool connects flexjoint to hull piping

Reduces bending moment at the riser vessel hang-off

49


VIV Suppression: Strakes/Fairings

Mitigation of VIV – Under long term and extreme currents

1 Strakes

(Courtesy of CRP)


1. Strakes– Typically polyurethane, fibreglass or plastic

2. Fairings– Typically fibreglass or plastic


Typical SCR Stress Outputs

015

0017

50s)

20-inch Gas Export 15 deg HO10-inch Production 14 deg HO8-inch Production 12 deg HO

8-inch Production 14 deg HO Typical Effective Tension Profile

0 2500 5000 7500 10000 12500 15000Curvilinear Distance along the set SCR (feet)

025

050

075

010

0012

50E

ffect

ive

Tens

ion

(kip

s

2530

35is

es S

tres

s (k

si)

20-inch Gas Export 15 deg HO10-inch Production 14 deg HO8-inch Production 12 deg HO

8-inch Production 14 deg HO

Touchdown


0 2500 5000 7500 10000 12500 15000Curvilinear Distance along the set SCR (feet)

510

1520

API

RP

2RD

von

Mi

Typical API RP 2RD Stress ProfileHang-Off

50


Fatigue Life Along SCR Length

100,000,000

1,000,000,000

10,000

100,000

1,000,000

10,000,000

, ,

Fatig

ue L

ife (y

ears

)

DirliksRayleigh

Hang-Off


100

1,000

10,000

0 500 1000 1500 2000 2500 3000 3500 4000 4500

Distance from Top of SCR (ft)

Hang OffSeabed

Touchdown


SCR Touchdown Fatigue

Behaviour at SCR touchdown point (TDP) key p ( ) ydesign driver

Fatigue

TDP response source of


design uncertaintySoil propertiesLimitations of soil models

51


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• Not be desirable along SCRs• Not be desirable along SCRs

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.

52


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


ElectricityDirect heatingSkin effectInduction

Mixed approach combining the two technical solutions described above


Riser Concepts – Flow Assurance1. SCR / Riser Tower

With or without wet insulation

2 Pipe-in-pipe (PIP) SCR2. Pipe-in-pipe (PIP) SCRImproved Flow AssuranceSignificantly heavier

3. Flexible Pipe w/ insulationProven design & track record

4. Integrated Production Bundle (IPB)Integrated Gas Lift, heating and services


g , gEvolving technology – based on flexible pipe

5. Integrated Production Umbilical (IPU)Integrated Gas Lift, heating and servicesEvolving technology – based on SCR

53


Riser Concepts (continued)6. Single Leg Hybrid Riser (SLHR) – Single Pipe

With or without wet insulationCombines steel and flexible pipe

7. Single Leg Hybrid Riser (SLHR) – Pipe-in-PipeDry insulation

8. Hybrid Bundle Riser (SLHR)Wet insulated bundle


9. Top Tensioned Riser (TTR)


Integrated Production Bundle (1)External Plastic Sheath

Thermal Insulation

Tubes forHot Water or/and Gas Lift


Flexible Riser Structure

Technip Patent

54


Integrated Production Bundle (2)


Courtesy Technip


Riser Solutions – Flow Assurance


55


Integrating Riser Design & Flow Assurance

Key items of integrationInsulation and its impact on riser drag-to-weight ratioRiser slugging and its impact on riser dynamics and ultimatelyRiser slugging and its impact on riser dynamics and ultimately fatigue damage

Deep Water Steel Catenary Riser ExampleHow does riser shape influence slugging?How does slugging affect fatigue life?

Methodology of InvestigationPerform slugging analysis with multiphase transient flow assurance software


Link flow assurance output with riser dynamics software and compute response

Key FindingsSlugging can have significant fatigue damage and depends of type of slugging and inclination of flowline into riser


Flow Assurance & Riser Dynamics

Riser Insulation:Increases outside diameter of pipe at lower density levels

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


Insulation increases the DTW valueLimit on amounts of insulation for catenary risers

Effective Tension is important for buoyant and top tensioned risers

56


Flow Assurance & Riser Dynamics

Riser Slugging:Impact of riser shape on sluggingImpact of riser shape on sluggingImpact of riser slugging on riser fatigue

Force terms from:changes in pressure and densitycentripetal due to slug velocity along curved riser


risercoriolis due to fluid motion in the moving riser frame of reference


Slugging CharacterisationWADO - Slugging Example - PPL Data

10" Flowline, Downslope, 20000 BPD, 90% Water Cut, 150 Sm3/Sm3Slug Length Profiles (4x)

800

300

400

500

600

700

1.00 hours1.25 hours1.50 hours1.75 hours2.00 hours2.25 hours2.50 hours2.75 hours3.00 hours


0

100

200

15000 16000 17000 18000 19000 20000 21000 22000 23000 24000 25000 26000 27000 28000

Distance (feet)

Time, length and location of slugs

57


Riser Model Discretisation

15 mSect 1

15 mSect 2

15 mSect 3

SLUG

Riser discretisation for slug force computation

WADO - SCR Touchdown Point Fatigue Enhancements10" Catenary Riser Profile

-1250

-1000

-750

-500

-250

0

TOPSIDES

RISER_1ARISER_1C

RISER_1B

RISER_2RISER_2C

RISER_2B

RISER_3

RISER_3

RISER_3

RISER_3

RISER_2D

RISER_1D

Riser section identification

Force terms computed from fluid pressure and density changes centripetal and


-2500

-2250

-2000

-1750

-1500

0 250 500 750 1000 1250 1500 1750 2000 2250

Distance from FPSO, m

changes, centripetal and coriolis forces due to slug / riser motions


Coupled vs Uncoupled Motions•Coupled Motion Analysis (Hydrodynamic coupling)

•(QTFs, wave forces RAOs, current & wind force coefficients, radiation damping & added matrices)•Required if inertia, damping, stiffness of risers & mooring significantly affectRequired if inertia, damping, stiffness of risers & mooring significantly affect response of host facility


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

Prescribed Motions

58


Installation Vessels - SCRs

J-Lay


Reel Lay

MSc in Subsea EngineeringInstallation, Schedule, Cost Drivers

Steel Riser and FlowlineInstallationS-lay

used up to moderately deep water, modified stinger for very deep waterlimit is curvature induced at stinger

J-laydeep to ultra-deep water riser installation, typically expensive option

Reel-layFaster 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)

59

MSc in Subsea EngineeringRiser & Flowline System SelectionImpact 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

B dl i t ll ti t i ll b t t


– Bundle installation typically by tow-out– SLHR installation may be pipelay vessel or MODU installation

MSc in Subsea EngineeringInstallation Challenges and VesselCapacity

● Installation ChallengesUltra-deepwater high tension loadsLarge diameterLarge diameterPositioning for TDP & clashing during transferRigging/handling of pull-in/abandonmentWeather fatigue during installationVessel on-site vs. abandonment & recovery (A&R)

● Installation Vessel Capacities:Max. Pipe

L TLay tension

V lC


60S2,500SolitaireAllseas32J1160S-7000Saipem60 (S), 18 (R)S, R1200HerculesGlobal

28R, J1697Deep BlueTechnip30J2800BalderHeerema

pSize (in)

Lay Typey(kips)

VesselCompany

Based on Reported Tension Capacities (2003)

60


Procurement & Installation Costs

Procurement Costs– Line Pipe or flexible pipe– Corrosion Protection coatingsCorrosion Protection coatings– 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 TypesTTRs, Flexibles, SCRs, Hybrids

Ri F d t lRiser FundamentalsTension / Bending, Effective TensionLarge displacementsTime Domain vs Frequency Domain

Extreme vs FatigueVessel motions

Touchdown bucklingTh l id ti


Thermal considerationsRiser Design and Flow AssuranceDrag-to-Weight RatioInstallation

61


Key Messages

Dry tree vs wet tree: Tensioned vs Compliant

Riser TypesypTTRs, Flexibles, SCRs, Hybrids

Riser FundamentalsLarge displacement, effective tension, equations of motion, time vsfrequency domain

Riser Design ConsiderationsVessel motionsTouchdown response and buckling


Touchdown response and bucklingFlexible pipe design issues and failure modesSCR design issues: touchdown and top connection flex/stress jointInternal flow regime and insulationCross-section impact on global motionsCoupled vessel-mooring-riser response


The End

Any Questions?


riser overview lecture feb 2011

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