Engineering Aspects of Engineering Aspects of Offshore Heavy Offshore Heavy - - Lift & Lift & Transportation Transportation Presentation to Aberdeen Presentation to Aberdeen IStructE IStructE 24 24 th th February 2005 February 2005 Jon Jon Dunstan Dunstan
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Engineering Aspects of Offshore Heavy Heavy-Lift & Transportation
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Engineering Aspects of Engineering Aspects of Offshore HeavyOffshore Heavy--Lift & Lift &
TransportationTransportation
Presentation to Aberdeen Presentation to Aberdeen IStructEIStructE2424thth February 2005February 2005
Jon Jon DunstanDunstan
IntroductionIntroduction
Just Just before before the final positioning at sea, production the final positioning at sea, production platforms for the exploration of oil and natural gas are platforms for the exploration of oil and natural gas are now now assembled almost to the point of completion. assembled almost to the point of completion. This This approachapproach requires the ability to move and lift large and requires the ability to move and lift large and heavy items at the yardheavy items at the yard as well as transporting them as well as transporting them by sea to their final location and installing them on the by sea to their final location and installing them on the seabed.seabed.
Industry has evolved to provide the tools and methodsIndustry has evolved to provide the tools and methodsto facilitate this high level of completion. Work offshoreto facilitate this high level of completion. Work offshorecan cost 10 x cost of onshore.can cost 10 x cost of onshore.
The Driving factorsThe Driving factorsPlatform Designer & FabricatorPlatform Designer & Fabricator--Minimise steel and equipment required for transport/installationMinimise steel and equipment required for transport/installation phases phases --Maximise onshore hookMaximise onshore hook--up and completionsup and completions
Transport & Installation (T&I) ContractorTransport & Installation (T&I) Contractor--Simplify lifts as far as possibleSimplify lifts as far as possible--maximise access and flexibility for marine operationsmaximise access and flexibility for marine operations--Minimise weather sensitivityMinimise weather sensitivity--Minimise danger to marine equipmentMinimise danger to marine equipment--maximise onshore preparationmaximise onshore preparation
OperatorOperator--Perform safe and quick installation, minimise riskPerform safe and quick installation, minimise risk--Minimise time between installation to first oilMinimise time between installation to first oil--Maximise efficiency/costMaximise efficiency/cost
The Basic stepsThe Basic steps1.Design & Fabricate Structure Onshore
2.Hook-up & Commission as a far as possible
3.Transfer (Load-out) structure onto barge/vessel for ocean tow
4.Tow to construction location in the field
5. Remove structures from barge and position in field
6. Secure structure in position
7. Offshore Hook-Up, testing & Commissioning
8. Operation
9. Shutdown, decommissioning and removal
STEPS 1 TO 3 – DESIGNER/FABRICATOR
STEPS 4 TO 6 – TRANSPORT & INSTALLATION (T&I) CONTRACTOR
STEPS 7 TO 8 – PLATFORM OPERATOR
Offshore StructuresOffshore StructuresPushing the limitsPushing the limits
1000'
3000'
5000'
2000'
4000'
6000'
FIXEDPLATFORM
FPSO
COMPLIANTTOWER
FPS
TLP
SUBSEACOPLETIONTh e d e e p e s t o f t h e d e e p
SPAR
1000 ft
4000 ft
3000 ft
2000 ft
5000 ft
6000 ft
History of Construction MethodsHistory of Construction Methods
A need for increased capacity and specialist tools. A step chanA need for increased capacity and specialist tools. A step change in design.ge in design.The birth of the semiThe birth of the semi--submersible crane vessel (SSCV) submersible crane vessel (SSCV) -- 6,3506,350 mtmt lift capacitylift capacity
need to design jackets for launch need to design jackets for launch
--Modules can be mechanically complete & commissionedModules can be mechanically complete & commissioned•• 2 lifts only (1 x jacket, 1 x deck)2 lifts only (1 x jacket, 1 x deck)
DESIGNING & PREPARING FOR PLATFORM TRANSPORT & INSTALLATION
PreparationPreparation•• OPERATIONALOPERATIONAL
•• Structure weighingStructure weighing•• Dimensional Control Dimensional Control
ChecksChecks•• Preinstall Lift RiggingPreinstall Lift Rigging•• Barge/vessel ArrivalBarge/vessel Arrival•• Barge Vessel MooringBarge Vessel Mooring•• Barge outfitting of Barge outfitting of
grillagegrillage•• Installation of Installation of linkspanlinkspan•• Transfer of Structure to Transfer of Structure to
quayside
•• DESIGNDESIGN
•• All temporary phases (All temporary phases (loadoutloadout, , transport, lift, ontransport, lift, on--bottom bottom stability, launch) assessed for stability, launch) assessed for strength strength
•• Local checks at interface pointsLocal checks at interface points•• Design of Grillage & Design of Grillage &
Preparations Before Preparations Before loadoutloadout
Preconnection of Lift Slings to padeyes/padears/trunnions
Rigging Laydown & securing
LoadoutLoadout
•• Transfer of structure from Transfer of structure from fabrication yard onto fabrication yard onto barge/vesselbarge/vessel
•• Method of Method of loadoutloadout--LiftedLifted--SkiddedSkidded--Trailers (SPMT)Trailers (SPMT)
•• Ballasting of barge to maintain Ballasting of barge to maintain level platform between level platform between quayside and barge deckquayside and barge deck
Assessment of Assessment of Loadout Loadout ConditionCondition•• Reactions from trailers (onto structure)Reactions from trailers (onto structure)•• Calculation of No. of trailers required (Calculation of No. of trailers required (typtyp. 30mt/axle). 30mt/axle)•• Skidshoe Skidshoe design/reactionsdesign/reactions-- required winch/strand jack required winch/strand jack
capacity/design of anchor pointscapacity/design of anchor points•• Influence of accelerationInfluence of acceleration•• Overall StabilityOverall Stability•• Physical clearancesPhysical clearances•• Link span end reactions check on barge & quayLink span end reactions check on barge & quay•• Link span strengthLink span strength•• UDL loads on quay, UDL loads on quay, linkspan linkspan and barge from trailersand barge from trailers•• (standard barge capacity, 10(standard barge capacity, 10--15mt/m15mt/m22))
SetSet--Down on BargeDown on BargeIntroductionIntroduction
•• Gradual Load Transfer Gradual Load Transfer onto Barge ‘Grillage’ onto Barge ‘Grillage’
•• Packing/shimming for Packing/shimming for even load distribution (up even load distribution (up to 48 support points)to 48 support points)
•• Acceptance by structure Acceptance by structure designerdesigner
•• Barge ballasted to ‘mimic Barge ballasted to ‘mimic tow’tow’
Design of Grillage & Design of Grillage & Seafastening Seafastening (1)(1)•• LoadsLoads--StaticStatic--DynamicDynamic--Lift/launchLift/launch--Deck SetDeck Set--down /matingdown /mating--FatigueFatigue--Wave slamWave slam--Details for simple removal Details for simple removal
-Conservative (Pitch (B or S) +/- heave, Roll ( P or S) +/- heave)
Design of Grillage &Design of Grillage &SeafasteningSeafastening (3)(3)
Noble Denton ’20 & 10’ Noble Denton ’20 & 10’ –– calculation of forces at calculation of forces at cargo cargo CoG CoG for Rollfor Roll
Design of Grillage &Design of Grillage &SeafasteningSeafastening (3)(3)Seafastening Seafastening DesignDesign
•• Dynamic loads only (Takes Dynamic loads only (Takes Fh Fh only)only)•• Generally taken axially in braces or in bearing via ‘shear stopsGenerally taken axially in braces or in bearing via ‘shear stops’’•• Any resulting couple taken as vertical loads through grillageAny resulting couple taken as vertical loads through grillage•• Allow 33% over normal allowable API/AISC stressesAllow 33% over normal allowable API/AISC stresses•• Gusset connections for easy removal (single plane strength only)Gusset connections for easy removal (single plane strength only)•• Possibility of roll ‘relief’ or roll ‘addition’Possibility of roll ‘relief’ or roll ‘addition’
Barge/Vessel Strength Barge/Vessel Strength
•• Support structure Support structure (grillage) to transfer (grillage) to transfer static loads and static loads and proportion of dynamic proportion of dynamic loads into barge/vessel loads into barge/vessel superstructuresuperstructure
•• Identification of barge Identification of barge transverse & longitudinal transverse & longitudinal frame capacitiesframe capacities
•• Grillages span Grillages span hardpointshardpoints•• Hog/Sag conditions for Hog/Sag conditions for
long structures (barge long structures (barge bending ‘encouraged’)bending ‘encouraged’)
Transport to FieldTransport to Field
Considerations:
-Distance
-Duration
-Cost
-risk
-Vessel cost &
availability
Self Propelled Vessel
Tug & Barge
Jackets (Lift)Jackets (Lift)
Single Crane Lift Tandem (Dual Crane) Lift
Upending sequenceUpending sequence
Jackets (Launch)Jackets (Launch)
Barge Ballasted to stern Launch over stern Hook-Assisted Upend