-
2H O
ffsh
ore
-dee
p w
ater
ris
er e
ngin
eeri
ng
Effects of High Temperature on the Design of Deepwater
Risers
March 2003
2H Offshore Engineering
-
2H O
ffsh
ore
-dee
p w
ater
ris
er e
ngin
eeri
ng
Outline of Talk
Overview of Riser SystemsWhat is High Temperature?High
Temperature (HT) DevelopmentsIssues Relating to SteelEffect on
Insulation MaterialsProblems with H2S, corrosion and fatigue
issuesBuoyancy IssuesPipe-In-Pipe SystemsUse of Flexible Jumpers
for COR & SLORSummary of HT Design IssuesAlternative Options
for Dealing with HP/HT
-
2H O
ffsh
ore
-dee
p w
ater
ris
er e
ngin
eeri
ng
Riser Systems - Configurations
Free Standing RisersSingle line
Bundled
Catenary RisersFlexible
Steel
Top Tensioned
-
2H O
ffsh
ore
-dee
p w
ater
ris
er e
ngin
eeri
ng
Riser Systems - Pipe Options
Flexible
Steel Pipe Non Insulated
Steel Pipe Insulated
Steel Pipe in Pipe
Bundled Steel Pipes
-
2H O
ffsh
ore
-dee
p w
ater
ris
er e
ngin
eeri
ng
What is High Temperature?
Typical production temperatures 40-80 deg C
High temperature 80 deg C - 100 deg C
Very high temperature 100 deg C +
-
2H O
ffsh
ore
-dee
p w
ater
ris
er e
ngin
eeri
ng
Current 2H HT Project Involvement
High
Very High
Very High
Production Pressure
TFEVery HighMoho Bilondo, Congo,600m
bpVery HighThunder Horse, GoM, 1800m
ChevronTexacoVery HighTahiti, GoM800m
OperatorProduction Temperature
Field
-
2H O
ffsh
ore
-dee
p w
ater
ris
er e
ngin
eeri
ng
Steel - Effect of High Temperature
Reduced yield strength at high temperatureAPI derating for T
> 120C (250F)
150C = 4.5% strength reductionDNV derating for T > 50C (120
F)
150 C = 30MPa strength reduction (5.5% on X80)
Example:steel manufactured to X70 Normal operating stress checks
performed against 65ksi to account for steel derating at HTStress
checks for shut-down conditions checked against 70ksi yield
strength since no HT
-
2H O
ffsh
ore
-dee
p w
ater
ris
er e
ngin
eeri
ng
Insulation Materials Effect of HT
Why would risers for HT wells need thermal insulation?Cool down
times during shut-in must be long enough to prevent hydrate
formation
-
2H O
ffsh
ore
-dee
p w
ater
ris
er e
ngin
eeri
ng
Insulation - RequirementsMeet thermal requirements
Steady state conditions (U-value) and specific heat
capacityMaintain temp. above critical value during shut-in
(12-24hrs)
Long-term hydrothermal stabilityMaintain material properties in
the long-term (20years)Water depth dictates compressive strength
and water absorption rates
DensityIncreases with increase water depth and
temperatureIncrease in density increases thermal conductivity
(k)Desire to keep riser weight and k-value low Increased tension,
drag loading, fatigue
-
2H O
ffsh
ore
-dee
p w
ater
ris
er e
ngin
eeri
ng
Insulation - Requirements
Corrosion protection & adhesionFBE typically used
mechanically bonds insulation to pipeAt high temperatures (>110
deg C) ordinary epoxy not suitable and high temperature epoxy
requiredResist cathodic disbondment if insulation coating is
damaged
Dynamic serviceResistant to cracking under fatigue loadingResist
large strains during storm loading and installation (S-lay, J-lay
and reeling)
Impact strengthResistant to crushing and mechanical strength
during storage and laying with tensioners and over stinger
rollers
-
2H O
ffsh
ore
-dee
p w
ater
ris
er e
ngin
eeri
ng
Insulation Material Selection
3 major types available for deep and ultra deepwater riser
application
Epoxy based syntactic foamsPolyurethane based syntactic
foamsMulti-layer polypropylene systems
Selection influenced by:Design temperatureManufacturability of
resulting insulation thickness based on required U-value and cool
down time (lower k-value gives lower insulation thickness)Cost
-
2H O
ffsh
ore
-dee
p w
ater
ris
er e
ngin
eeri
ng
Insulation - Epoxy Syntactic Foams
Composite - fiberglass macro spheres in an epoxy binderCast
directly onto pipeLow density (600 kg/m3 at 1200m)High thermal
efficiency (k = 0.09 W/m.K at 1200m depth)Low costLess flexible
than PU or PP (cracking concern in high fatigue areas)Limited to
100 deg C serviceUsed on 1000m GoM Shell King (1999) with 6 miles
of C-THERM for 6 OD flowlines (80 deg C design temp.)Limited riser
track record
C-Therm with macrospheres
-
2H O
ffsh
ore
-dee
p w
ater
ris
er e
ngin
eeri
ng
Insulation - PU Syntactic Foams
Polyurethane matrix loaded with gas filled glass micro
spheresApplied by standard molding techniquesHigher density
compared with epoxy syntactic foams (800 kg/m3 at 1200m)Moderate
thermal efficiency (k = 0.165 W/m.K at 1200m depth)Medium
costLimited to 90 deg C serviceUsed on 1600m GoM BP King (2001)
with 59km of GSPU for 12 OD flowlines (83 deg C design
temp.)Limited riser track record
Glass Syntactic Polyurethane(GSPU)
-
2H O
ffsh
ore
-dee
p w
ater
ris
er e
ngin
eeri
ng
Insulation - Multi-layer Polypropylene (PP)
3-layer corrosion barrier plus PP foam insulation and solid PP
shieldApplied by side or cross extrusion processHigher density (800
kg/m3 at 1200m)Moderate thermal efficiency (k = 0.13 to 0.22
W/m.K)Medium / highest costHigh temp service up to 140 deg C Used
on:
1500m GoM BP Nile (2000) with Thermotitefor 6 OD SCR (90 deg C
design temp.)Asgard flowlines (140 deg C design temp.)
Will be used for:GoM BP Thunder Horse production SCRs
5-layer Thermotite System
-
2H O
ffsh
ore
-dee
p w
ater
ris
er e
ngin
eeri
ng
Insulation - Field Joints System Quality
Specialist joints made in factory for main riser lengths but
same quality also needed for field jointsIf high quality field
joint are not achieved:
Water ingressCorrosion - pitting- fatigueReduced insulation cold
spotConvection cold spot
Minimise number of field joints since costly due to
Speed of assemblyProblems associated with working on the
vessel
-
2H O
ffsh
ore
-dee
p w
ater
ris
er e
ngin
eeri
ng
Insulation - Material Qualification
Little long-term data available for high temp. serviceTesting
required for successful applicationSmall scale hydrothermal ageing
tests under pressure, accelerated using an elevated temperature
(least expensive)Large scale pipe simulated service tests to
determine thermal performance and long-term degradation
(expensive)Mechanical tests (tensile, shear, bend, adhesion, impact
and fatigue)Cathodic disbondment
-
2H O
ffsh
ore
-dee
p w
ater
ris
er e
ngin
eeri
ng
H2S Effect on Fatigue Performance
Recent tests at 60deg C indicate significant reduction in
fatigue performance if H2S present (Factor of 20 on life)Effects of
HT are currently unknown
-
2H O
ffsh
ore
-dee
p w
ater
ris
er e
ngin
eeri
ng
Corrosion Effects at High Temperatures
Rate of corrosion increases with increase in temp. due to
reduced efficiency of cathodic protection systemTherefore require
more anode mass and/or reduced spacing of anodesIntegrity of
coating barriers also an issue at HTTherefore corrosion allowances
must increase thicker walled pipesImpact on cost and weight
-
2H O
ffsh
ore
-dee
p w
ater
ris
er e
ngin
eeri
ng
Corrosion Effect on Stresses and Fatigue
Calculation of stresses in riser need to take account of
potential wall thickness loss due to corrosion
Corrosion allowances may lead to thick-walled pipes and wall
thickness correction factor must be applied when assessing fatigue
performance (DnV 2001 > 25mm)
-
2H O
ffsh
ore
-dee
p w
ater
ris
er e
ngin
eeri
ng
Fatigue Life Enhancement
Low fatigue lifes due to high corrosion levels etc. may be
improved by:
Improve weld quality (double side weld)Reduce stresses using
upset (thickened end) pipe Overlay of critical welds with corrosion
resistance alloy (CRA)Reduce stresses using external sleeves
Cost Increase
-
2H O
ffsh
ore
-dee
p w
ater
ris
er e
ngin
eeri
ng
Buoyancy - Typical Properties
Temperature toleranceWater ingress
-
2H O
ffsh
ore
-dee
p w
ater
ris
er e
ngin
eeri
ng
Buoyancy/Insulation - Hot / Wet Issues
Accelerated water permeationLoss of buoyancyLoss of
insulation
SolutionUse of pure syntactics - no spheres- (heavy)Use of
resistant materials Amines (costly)Low permeability coatings
polyethylene (damage)Barrier insulation material temp. gradient
(complex)Bonding direct to pipe to prevent hot/wet (not practical
with bundles)
-
2H O
ffsh
ore
-dee
p w
ater
ris
er e
ngin
eeri
ng
Buoyancy/Insulation - Conventional Bundle
Hot/Wet interfaceComplex buoyancy profile
Difficulty castingNumber of piecesAssembly procedure
Poor heat sharing
-
2H O
ffsh
ore
-dee
p w
ater
ris
er e
ngin
eeri
ng
Buoyancy/Insulation - Internal Bundle
Buoyancy Modules
Carrier Pipe
Production Flowlines
Encircling Water
Production Fluid
Gel Medium
-
2H O
ffsh
ore
-dee
p w
ater
ris
er e
ngin
eeri
ng
Buoyancy/Insulation - Internal Bundle Riser
Lower buoyancy contact temperature Better heat sharing between
prod. linesAbility to circulate cooler waterAbility to circulate
hot waterSimpler buoyancy shapesLower buoyancy material
spec.Similar thermal expansion
-
2H O
ffsh
ore
-dee
p w
ater
ris
er e
ngin
eeri
ng
PIP, TTR and COR - HT Issues
For pipe-in-pipe (PIP), top tensioned risers (TTR) and
concentric offset risers (COR)Different pipes are at different
temperatures and the relative thermal expansion of pipes must be
considered:
Inner pipe expansionBucklingCentraliser design and
spacingPreloadingCrushing of insulation Cold spots
Friction
Centraliser Spacing
Tension
Compression
-
2H O
ffsh
ore
-dee
p w
ater
ris
er e
ngin
eeri
ng
Flexible Jumpers - Free Standing Risers
Difficult to design CORs /SLORs for HT due to problems with
flexible jumpers
Internal pressure sheathEnd fittingsStiffener design
-
2H O
ffsh
ore
-dee
p w
ater
ris
er e
ngin
eeri
ng
Flexible Jumpers Internal Pressure Sheath
Material Temp. Range (C) Water Cut
(%) Comments
HDPE -50 to +60 0 - 100 High tensile and impact resistance at
low temp and low pressure
XLPE -50 to +90 0 100 Upper temperature limit reduces if
pressure >2000psi -20 to +100 0
-20 to +90 0 5 PA-11
-20 to +65 5 - 100
Weak resistance to high water cut at HT
PVDF -20 to +130 0 100 Appropriate for HP/HT applications
Maximum operating temperature is highly dependent on the design
life of the pipe
-
2H O
ffsh
ore
-dee
p w
ater
ris
er e
ngin
eeri
ng
Flexible Jumpers Internal Pressure Sheath
Example using PA-11:Design life of 30-years operating
temperature 55CDesign life of 10-years - operating temperature
70CDesign life of 1-year operating temperature 100C
-
2H O
ffsh
ore
-dee
p w
ater
ris
er e
ngin
eeri
ng
Flexible Jumpers End Fitting Design
When PVDF used as internal pressure sheath:End-fitting design
(crimping/sealing mechanism) is criticalPotential for plasticizer
loss is high reduced seal efficiencyPVDF has higher thermal
expansion coefficient cyclic expansion/contraction gradual pull-out
of sheath from end fittingSignificant development by manufacturers
mean these issues are being addressed and continual improvements
are made
-
2H O
ffsh
ore
-dee
p w
ater
ris
er e
ngin
eeri
ng
Flexible Jumpers Stiffener Design
Stiffener at connection jumper/manifold is made from structural
polyurethane (PU)
PU susceptible to aging at relatively low temp. (e.g. 50 C)
therefore need to accurately determine stiffener internal wall
temperatureTemperatures can be reduced by using water circulation
around stiffener or active cooling
-
2H O
ffsh
ore
-dee
p w
ater
ris
er e
ngin
eeri
ng
Flex Joint Issues at HT
Design IssuesAging of rubber at HTRapid decompression at HP
SolutionCRA Bellows (pressure balanced)Prevents direct contact
of rubber with hydrocarbonsProduces temperature gradient across
bellowsReduces rubber temperature
ImpactCostAdditional stiffnessFatigue of bellows
-
2H O
ffsh
ore
-dee
p w
ater
ris
er e
ngin
eeri
ng
Summary of Riser Design Issues at HT
HT wells result in additional complexity for riser design
Material performance derating of steel yield strengthProblems
with buoyancy / insulation material at HTPotential issues with H2S
(if present)Accelerated corrosion ratesKnock on effects on riser
wall thicknesses and fatigueAdditional considerations for
pipe-in-pipe systemsIssues for flexible pipesIssue for key
components such as flex-joint design
These all results in significant increase in riser cost due to
higher spec. materials, increase weight etc.
Attention should be turned to finding alternative ways of
dealing with HP/HT problem
Attention should be turned to finding alternative Attention
should be turned to finding alternative ways of dealing with HP/HT
problemways of dealing with HP/HT problem
-
2H O
ffsh
ore
-dee
p w
ater
ris
er e
ngin
eeri
ng
Alternative Approach for HP/HT Risers
High TemperatureCooling loops or heat exchanges on
seabedPotential problems with hydrates and wax in exchanger during
shut down can be solved with chemicalsTherefore high temperature
issues with insulation/buoyancy, steel etc. are no longer a
problemThis approach is yet to be implemented
High PressureHigh Integrity Pressure Protection System
(HIPPS)Complex control and additional subsea valving/choking to
reduce pressure in riser systemIssues relating to reliability and
risk must be addressedAlready implemented on a number of
systems
-
2H O
ffsh
ore
-dee
p w
ater
ris
er e
ngin
eeri
ng
Alternative Approach for HP/HT Risers
Use both cooling loops and HIPPS to eliminate problems with
HP/HT risers. Benefits include:
Reduce weight of riserReduce vessel payload / buoyancy
requirementsReduce insulation/buoyancy material issuesFaster
installationReduced hydrodynamic drag Improved dynamic
responseLower quality welding may be acceptable
