Offshore platform design
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07/30/2003 OFFSHORE
PLATFORM DESIGN
WELCOMEWELCOME
PRESENTATION ON PRESENTATION ON
OFFSHORE PLATFORM DESIGNOFFSHORE PLATFORM DESIGN
PLATFORM DESIGN
WELCOMEWELCOME
PRESENTATION ON PRESENTATION ON
OFFSHORE PLATFORM DESIGNOFFSHORE PLATFORM DESIGN
07/30/2003 OFFSHORE
PLATFORM DESIGN
Welcome aboard exciting world of Offshore platforms design. In Next 45 Welcome aboard exciting world of Offshore platforms design. In Next 45
minutes we will take you to educational trip of offshore platforms with minutes we will take you to educational trip of offshore platforms with
breathtaking views and path breaking engineering accomplishments. breathtaking views and path breaking engineering accomplishments.
PLATFORM DESIGN
Welcome aboard exciting world of Offshore platforms design. In Next 45 Welcome aboard exciting world of Offshore platforms design. In Next 45
minutes we will take you to educational trip of offshore platforms with minutes we will take you to educational trip of offshore platforms with
breathtaking views and path breaking engineering accomplishments. breathtaking views and path breaking engineering accomplishments.
07/30/2003 OFFSHORE
PLATFORM DESIGN
OVERVIEWOVERVIEW
Offshore platforms are used for Offshore platforms are used for
exploration of Oil and Gas from exploration of Oil and Gas from
under Seabed and processing.under Seabed and processing.
The First Offshore platform was The First Offshore platform was
installed in 1947 off the coast of installed in 1947 off the coast of
Louisiana in 6M depth of water. Louisiana in 6M depth of water.
Today there are over 7,000 Today there are over 7,000
Offshore platforms around the Offshore platforms around the
world in water depths up to world in water depths up to
1,850M1,850M
PLATFORM DESIGN
OVERVIEWOVERVIEW
Offshore platforms are used for Offshore platforms are used for
exploration of Oil and Gas from exploration of Oil and Gas from
under Seabed and processing.under Seabed and processing.
The First Offshore platform was The First Offshore platform was
installed in 1947 off the coast of installed in 1947 off the coast of
Louisiana in 6M depth of water. Louisiana in 6M depth of water.
Today there are over 7,000 Today there are over 7,000
Offshore platforms around the Offshore platforms around the
world in water depths up to world in water depths up to
1,850M1,850M
07/30/2003 OFFSHORE
PLATFORM DESIGN
OVERVIEWOVERVIEW
Platform size depends on facilities to be Platform size depends on facilities to be
installed on top side eg. Oil rig, living installed on top side eg. Oil rig, living
quarters, Helipad etc.quarters, Helipad etc.
Classification of water depths:Classification of water depths:
–< 350 M- Shallow water< 350 M- Shallow water
–< 1500 M - Deep water< 1500 M - Deep water
–> 1500 M- Ultra deep water > 1500 M- Ultra deep water
–US Mineral Management Service US Mineral Management Service
(MMS) classifies water depths greater (MMS) classifies water depths greater
than 1,300 ft as deepwater, and greater than 1,300 ft as deepwater, and greater
than 5,000 ft as ultra-deepwater.than 5,000 ft as ultra-deepwater.
PLATFORM DESIGN
OVERVIEWOVERVIEW
Platform size depends on facilities to be Platform size depends on facilities to be
installed on top side eg. Oil rig, living installed on top side eg. Oil rig, living
quarters, Helipad etc.quarters, Helipad etc.
Classification of water depths:Classification of water depths:
–< 350 M- Shallow water< 350 M- Shallow water
–< 1500 M - Deep water< 1500 M - Deep water
–> 1500 M- Ultra deep water > 1500 M- Ultra deep water
–US Mineral Management Service US Mineral Management Service
(MMS) classifies water depths greater (MMS) classifies water depths greater
than 1,300 ft as deepwater, and greater than 1,300 ft as deepwater, and greater
than 5,000 ft as ultra-deepwater.than 5,000 ft as ultra-deepwater.
07/30/2003 OFFSHORE
PLATFORM DESIGN
OVERVIEWOVERVIEW
Offshore platforms can broadly categorized in two typesOffshore platforms can broadly categorized in two types
Fixed structures that extend to the Seabed.Fixed structures that extend to the Seabed.
Steel JacketSteel Jacket
Concrete gravity StructureConcrete gravity Structure
Compliant TowerCompliant Tower
PLATFORM DESIGN
OVERVIEWOVERVIEW
Offshore platforms can broadly categorized in two typesOffshore platforms can broadly categorized in two types
Fixed structures that extend to the Seabed.Fixed structures that extend to the Seabed.
Steel JacketSteel Jacket
Concrete gravity StructureConcrete gravity Structure
Compliant TowerCompliant Tower
07/30/2003 OFFSHORE
PLATFORM DESIGN
OVERVIEWOVERVIEW
Structures that float near the water surface- Recent developmentStructures that float near the water surface- Recent development
Tension Leg platformsTension Leg platforms
Semi SubmersibleSemi Submersible
SparSpar
Ship shaped vessel (FPSO)Ship shaped vessel (FPSO)
PLATFORM DESIGN
OVERVIEWOVERVIEW
Structures that float near the water surface- Recent developmentStructures that float near the water surface- Recent development
Tension Leg platformsTension Leg platforms
Semi SubmersibleSemi Submersible
SparSpar
Ship shaped vessel (FPSO)Ship shaped vessel (FPSO)
OFFSHORE PLATFORM DESIGN07/30/2003
TYPE OF PLATFORMS (FIXED)TYPE OF PLATFORMS (FIXED)
JACKETED PLATFORMJACKETED PLATFORM
–Space framed structure with tubular Space framed structure with tubular
members supported on piled members supported on piled
foundations. foundations.
–Used for moderate water depths up to Used for moderate water depths up to
400 M.400 M.
–Jackets provides protective layer around Jackets provides protective layer around
the pipes.the pipes.
–Typical offshore structure will have a Typical offshore structure will have a
deck structure containing a Main Deck, deck structure containing a Main Deck,
a Cellar Deck, and a Helideck. a Cellar Deck, and a Helideck.
–The deck structure is supported by deck The deck structure is supported by deck
legs connected to the top of the piles. legs connected to the top of the piles.
The piles extend from above the Mean The piles extend from above the Mean
Low Water through the seabed and into Low Water through the seabed and into
the soil.the soil.
TYPE OF PLATFORMS (FIXED)TYPE OF PLATFORMS (FIXED)
JACKETED PLATFORMJACKETED PLATFORM
–Space framed structure with tubular Space framed structure with tubular
members supported on piled members supported on piled
foundations. foundations.
–Used for moderate water depths up to Used for moderate water depths up to
400 M.400 M.
–Jackets provides protective layer around Jackets provides protective layer around
the pipes.the pipes.
–Typical offshore structure will have a Typical offshore structure will have a
deck structure containing a Main Deck, deck structure containing a Main Deck,
a Cellar Deck, and a Helideck. a Cellar Deck, and a Helideck.
–The deck structure is supported by deck The deck structure is supported by deck
legs connected to the top of the piles. legs connected to the top of the piles.
The piles extend from above the Mean The piles extend from above the Mean
Low Water through the seabed and into Low Water through the seabed and into
the soil.the soil.
OFFSHORE PLATFORM DESIGN07/30/2003
TYPE OF PLATFORMS (FIXED)TYPE OF PLATFORMS (FIXED)
JACKETED PLATFORM (Cont.)JACKETED PLATFORM (Cont.)
–Underwater, the piles are contained Underwater, the piles are contained
inside the legs of a “jacket” structure inside the legs of a “jacket” structure
which serves as bracing for the piles which serves as bracing for the piles
against lateral loads. against lateral loads.
–The jacket also serves as a template The jacket also serves as a template
for the initial driving of the piles. for the initial driving of the piles.
(The piles are driven through the (The piles are driven through the
inside of the legs of the jacket inside of the legs of the jacket
structure).structure).
–Natural period (usually 2.5 second) Natural period (usually 2.5 second)
is kept below wave period (14 to 20 is kept below wave period (14 to 20
seconds) to avoid amplification of seconds) to avoid amplification of
wave loads.wave loads.
–95% of offshore platforms around 95% of offshore platforms around
the world are Jacket supported. the world are Jacket supported.
TYPE OF PLATFORMS (FIXED)TYPE OF PLATFORMS (FIXED)
JACKETED PLATFORM (Cont.)JACKETED PLATFORM (Cont.)
–Underwater, the piles are contained Underwater, the piles are contained
inside the legs of a “jacket” structure inside the legs of a “jacket” structure
which serves as bracing for the piles which serves as bracing for the piles
against lateral loads. against lateral loads.
–The jacket also serves as a template The jacket also serves as a template
for the initial driving of the piles. for the initial driving of the piles.
(The piles are driven through the (The piles are driven through the
inside of the legs of the jacket inside of the legs of the jacket
structure).structure).
–Natural period (usually 2.5 second) Natural period (usually 2.5 second)
is kept below wave period (14 to 20 is kept below wave period (14 to 20
seconds) to avoid amplification of seconds) to avoid amplification of
wave loads.wave loads.
–95% of offshore platforms around 95% of offshore platforms around
the world are Jacket supported. the world are Jacket supported.
OFFSHORE PLATFORM DESIGN07/30/2003
TYPE OF PLATFORMS (FIXED)TYPE OF PLATFORMS (FIXED)
COMPLIANT TOWERCOMPLIANT TOWER
–Narrow, flexible framed structures Narrow, flexible framed structures
supported by piled foundations. supported by piled foundations.
–Has no oil storage capacity. Production is Has no oil storage capacity. Production is
through tensioned rigid risers and export through tensioned rigid risers and export
by flexible or catenary steel pipe. by flexible or catenary steel pipe.
–Undergo large lateral deflections (up to 10 Undergo large lateral deflections (up to 10
ft) under wave loading. Used for ft) under wave loading. Used for
moderate water depths up to 600 M.moderate water depths up to 600 M.
–Natural period (usually 30 second) is kept Natural period (usually 30 second) is kept
above wave period (14 to 20 seconds) to above wave period (14 to 20 seconds) to
avoid amplification of wave loads.avoid amplification of wave loads.
TYPE OF PLATFORMS (FIXED)TYPE OF PLATFORMS (FIXED)
COMPLIANT TOWERCOMPLIANT TOWER
–Narrow, flexible framed structures Narrow, flexible framed structures
supported by piled foundations. supported by piled foundations.
–Has no oil storage capacity. Production is Has no oil storage capacity. Production is
through tensioned rigid risers and export through tensioned rigid risers and export
by flexible or catenary steel pipe. by flexible or catenary steel pipe.
–Undergo large lateral deflections (up to 10 Undergo large lateral deflections (up to 10
ft) under wave loading. Used for ft) under wave loading. Used for
moderate water depths up to 600 M.moderate water depths up to 600 M.
–Natural period (usually 30 second) is kept Natural period (usually 30 second) is kept
above wave period (14 to 20 seconds) to above wave period (14 to 20 seconds) to
avoid amplification of wave loads.avoid amplification of wave loads.
OFFSHORE PLATFORM DESIGN07/30/2003
TYPE OF PLATFORMS (FIXED)TYPE OF PLATFORMS (FIXED)
CONCRETE GRAVITY CONCRETE GRAVITY
STRUCTURES:STRUCTURES:
–Fixed-bottom structures made from concrete Fixed-bottom structures made from concrete
–Heavy and remain in place on the seabed Heavy and remain in place on the seabed
without the need for pileswithout the need for piles
–Used for moderate water depths up to 300 M.Used for moderate water depths up to 300 M.
–Part construction is made in a dry dock Part construction is made in a dry dock
adjacent to the sea. The structure is built from adjacent to the sea. The structure is built from
bottom up, like onshore structure.bottom up, like onshore structure.
–At a certain point , dock is flooded and the At a certain point , dock is flooded and the
partially built structure floats. It is towed to partially built structure floats. It is towed to
deeper sheltered water where remaining deeper sheltered water where remaining
construction is completed.construction is completed.
–After towing to field, base is filled with water After towing to field, base is filled with water
to sink it on the seabed. to sink it on the seabed.
–Advantage- Less maintenanceAdvantage- Less maintenance
TYPE OF PLATFORMS (FIXED)TYPE OF PLATFORMS (FIXED)
CONCRETE GRAVITY CONCRETE GRAVITY
STRUCTURES:STRUCTURES:
–Fixed-bottom structures made from concrete Fixed-bottom structures made from concrete
–Heavy and remain in place on the seabed Heavy and remain in place on the seabed
without the need for pileswithout the need for piles
–Used for moderate water depths up to 300 M.Used for moderate water depths up to 300 M.
–Part construction is made in a dry dock Part construction is made in a dry dock
adjacent to the sea. The structure is built from adjacent to the sea. The structure is built from
bottom up, like onshore structure.bottom up, like onshore structure.
–At a certain point , dock is flooded and the At a certain point , dock is flooded and the
partially built structure floats. It is towed to partially built structure floats. It is towed to
deeper sheltered water where remaining deeper sheltered water where remaining
construction is completed.construction is completed.
–After towing to field, base is filled with water After towing to field, base is filled with water
to sink it on the seabed. to sink it on the seabed.
–Advantage- Less maintenanceAdvantage- Less maintenance
OFFSHORE PLATFORM DESIGN07/30/2003
TYPE OF PLATFORMS (FLOATER)TYPE OF PLATFORMS (FLOATER)
Tension Leg Platform (TLP)Tension Leg Platform (TLP)
–Tension Leg Platforms (TLPs) are Tension Leg Platforms (TLPs) are
floating facilities that are tied down to floating facilities that are tied down to
the seabed by vertical steel tubesthe seabed by vertical steel tubes called called
tethers.tethers.
–This characteristic makes the structure This characteristic makes the structure
very rigid in the vertical direction and very rigid in the vertical direction and
very flexible in the horizontal plane. very flexible in the horizontal plane.
The vertical rigidity helps to tie in The vertical rigidity helps to tie in
wells for production, while, the wells for production, while, the
horizontal compliance makes the horizontal compliance makes the
platform insensitive to the primary platform insensitive to the primary
effect of waves.effect of waves.
–Have large columns and Pontoons and Have large columns and Pontoons and
a fairly deep draught. a fairly deep draught.
TYPE OF PLATFORMS (FLOATER)TYPE OF PLATFORMS (FLOATER)
Tension Leg Platform (TLP)Tension Leg Platform (TLP)
–Tension Leg Platforms (TLPs) are Tension Leg Platforms (TLPs) are
floating facilities that are tied down to floating facilities that are tied down to
the seabed by vertical steel tubesthe seabed by vertical steel tubes called called
tethers.tethers.
–This characteristic makes the structure This characteristic makes the structure
very rigid in the vertical direction and very rigid in the vertical direction and
very flexible in the horizontal plane. very flexible in the horizontal plane.
The vertical rigidity helps to tie in The vertical rigidity helps to tie in
wells for production, while, the wells for production, while, the
horizontal compliance makes the horizontal compliance makes the
platform insensitive to the primary platform insensitive to the primary
effect of waves.effect of waves.
–Have large columns and Pontoons and Have large columns and Pontoons and
a fairly deep draught. a fairly deep draught.
OFFSHORE PLATFORM DESIGN07/30/2003
TYPE OF PLATFORMS (FLOATER)TYPE OF PLATFORMS (FLOATER)
Tension Leg Platform (TLP)Tension Leg Platform (TLP)
–TLP has excess buoyancy which keeps TLP has excess buoyancy which keeps
tethers in tension. Topside facilities , tethers in tension. Topside facilities ,
no. of risers etc. have to fixed at pre-no. of risers etc. have to fixed at pre-
design stage. design stage.
–Used for deep water up to 1200 MUsed for deep water up to 1200 M
–It has no integral storage.It has no integral storage.
–It is sensitive to topside load/draught It is sensitive to topside load/draught
variations as tether tensions are variations as tether tensions are
affected.affected.
TYPE OF PLATFORMS (FLOATER)TYPE OF PLATFORMS (FLOATER)
Tension Leg Platform (TLP)Tension Leg Platform (TLP)
–TLP has excess buoyancy which keeps TLP has excess buoyancy which keeps
tethers in tension. Topside facilities , tethers in tension. Topside facilities ,
no. of risers etc. have to fixed at pre-no. of risers etc. have to fixed at pre-
design stage. design stage.
–Used for deep water up to 1200 MUsed for deep water up to 1200 M
–It has no integral storage.It has no integral storage.
–It is sensitive to topside load/draught It is sensitive to topside load/draught
variations as tether tensions are variations as tether tensions are
affected.affected.
OFFSHORE PLATFORM DESIGN07/30/2003
TYPE OF PLATFORMS (FLOATER)TYPE OF PLATFORMS (FLOATER)
SEMISUB PLATFORMSEMISUB PLATFORM
–Due to small water plane area , they are Due to small water plane area , they are
weight sensitive. Flood warning systems are weight sensitive. Flood warning systems are
required to be in-place.required to be in-place.
–Topside facilities , no. of risers etc. have to Topside facilities , no. of risers etc. have to
fixed at pre-design stage. fixed at pre-design stage.
–Used for Ultra deep water.Used for Ultra deep water.
–Semi-submersibles are held in place by Semi-submersibles are held in place by
anchors connected to a catenary mooring anchors connected to a catenary mooring
system.system.
TYPE OF PLATFORMS (FLOATER)TYPE OF PLATFORMS (FLOATER)
SEMISUB PLATFORMSEMISUB PLATFORM
–Due to small water plane area , they are Due to small water plane area , they are
weight sensitive. Flood warning systems are weight sensitive. Flood warning systems are
required to be in-place.required to be in-place.
–Topside facilities , no. of risers etc. have to Topside facilities , no. of risers etc. have to
fixed at pre-design stage. fixed at pre-design stage.
–Used for Ultra deep water.Used for Ultra deep water.
–Semi-submersibles are held in place by Semi-submersibles are held in place by
anchors connected to a catenary mooring anchors connected to a catenary mooring
system.system.
OFFSHORE PLATFORM DESIGN07/30/2003
TYPE OF PLATFORMS (FLOATER)TYPE OF PLATFORMS (FLOATER)
SEMISUB PLATFORMSEMISUB PLATFORM
–Column pontoon junctions and bracing Column pontoon junctions and bracing
attract large loads.attract large loads.
–Due to possibility of fatigue cracking of Due to possibility of fatigue cracking of
braces , periodic inspection/ braces , periodic inspection/
maintenance is prerequisitemaintenance is prerequisite
TYPE OF PLATFORMS (FLOATER)TYPE OF PLATFORMS (FLOATER)
SEMISUB PLATFORMSEMISUB PLATFORM
–Column pontoon junctions and bracing Column pontoon junctions and bracing
attract large loads.attract large loads.
–Due to possibility of fatigue cracking of Due to possibility of fatigue cracking of
braces , periodic inspection/ braces , periodic inspection/
maintenance is prerequisitemaintenance is prerequisite
OFFSHORE PLATFORM DESIGN07/30/2003
TYPE OF PLATFORMS (FLOATER)TYPE OF PLATFORMS (FLOATER)
SPAR:SPAR:
–Concept of a large diameter single vertical Concept of a large diameter single vertical
cylinder supporting deck.cylinder supporting deck.
–These are a very new and emerging concept: the These are a very new and emerging concept: the
first spar platform, first spar platform, NeptuneNeptune, was installed off , was installed off
the USA coast in 1997the USA coast in 1997.
–Spar platforms have taut catenary moorings and Spar platforms have taut catenary moorings and
deep draught, hence heave natural period is deep draught, hence heave natural period is
about 30 seconds.about 30 seconds.
–Used for Ultra deep water depth of 2300 M.Used for Ultra deep water depth of 2300 M.
–The center of buoyancy is considerably above The center of buoyancy is considerably above
center of gravity , making Spar quite stable.center of gravity , making Spar quite stable.
–Due to space restrictions in the core, number of Due to space restrictions in the core, number of
risers has to be predetermined.risers has to be predetermined.
TYPE OF PLATFORMS (FLOATER)TYPE OF PLATFORMS (FLOATER)
SPAR:SPAR:
–Concept of a large diameter single vertical Concept of a large diameter single vertical
cylinder supporting deck.cylinder supporting deck.
–These are a very new and emerging concept: the These are a very new and emerging concept: the
first spar platform, first spar platform, NeptuneNeptune, was installed off , was installed off
the USA coast in 1997the USA coast in 1997.
–Spar platforms have taut catenary moorings and Spar platforms have taut catenary moorings and
deep draught, hence heave natural period is deep draught, hence heave natural period is
about 30 seconds.about 30 seconds.
–Used for Ultra deep water depth of 2300 M.Used for Ultra deep water depth of 2300 M.
–The center of buoyancy is considerably above The center of buoyancy is considerably above
center of gravity , making Spar quite stable.center of gravity , making Spar quite stable.
–Due to space restrictions in the core, number of Due to space restrictions in the core, number of
risers has to be predetermined.risers has to be predetermined.
OFFSHORE PLATFORM DESIGN07/30/2003
TYPE OF PLATFORMS (FLOATER)TYPE OF PLATFORMS (FLOATER)
SHIP SHAPED VESSEL (FPSO)SHIP SHAPED VESSEL (FPSO)
–Ship-shape platforms are called Floating Ship-shape platforms are called Floating
Production, Storage and Offloading (FPSO) Production, Storage and Offloading (FPSO)
facilities. facilities.
–FPSOs have integral oil storage capability FPSOs have integral oil storage capability
inside their hull. This avoids a long and inside their hull. This avoids a long and
expensive pipeline to shore.expensive pipeline to shore.
–Can explore in remote and deep water and Can explore in remote and deep water and
also in marginal wells, where building also in marginal wells, where building
fixed platform and piping is technically and fixed platform and piping is technically and
economically not feasibleeconomically not feasible
–FPSOs are held in position over the FPSOs are held in position over the
reservoir at a Single Point Mooring (SPM). reservoir at a Single Point Mooring (SPM).
The vessel is able to weathervane around The vessel is able to weathervane around
the mooring point so that it always faces the mooring point so that it always faces
into the prevailing weather.into the prevailing weather.
TYPE OF PLATFORMS (FLOATER)TYPE OF PLATFORMS (FLOATER)
SHIP SHAPED VESSEL (FPSO)SHIP SHAPED VESSEL (FPSO)
–Ship-shape platforms are called Floating Ship-shape platforms are called Floating
Production, Storage and Offloading (FPSO) Production, Storage and Offloading (FPSO)
facilities. facilities.
–FPSOs have integral oil storage capability FPSOs have integral oil storage capability
inside their hull. This avoids a long and inside their hull. This avoids a long and
expensive pipeline to shore.expensive pipeline to shore.
–Can explore in remote and deep water and Can explore in remote and deep water and
also in marginal wells, where building also in marginal wells, where building
fixed platform and piping is technically and fixed platform and piping is technically and
economically not feasibleeconomically not feasible
–FPSOs are held in position over the FPSOs are held in position over the
reservoir at a Single Point Mooring (SPM). reservoir at a Single Point Mooring (SPM).
The vessel is able to weathervane around The vessel is able to weathervane around
the mooring point so that it always faces the mooring point so that it always faces
into the prevailing weather.into the prevailing weather.
OFFSHORE PLATFORM DESIGN07/30/2003
PLATFORM PARTSPLATFORM PARTS
TOPSIDE:TOPSIDE:
–Facilities are tailored to achieve Facilities are tailored to achieve
weight and space savingweight and space saving
–Incorporates process and utility Incorporates process and utility
equipment equipment
Drilling RigDrilling Rig
Injection CompressorsInjection Compressors
Gas CompressorsGas Compressors
Gas Turbine GeneratorsGas Turbine Generators
PipingPiping
HVACHVAC
InstrumentationInstrumentation
–Accommodation for operating Accommodation for operating
personnel.personnel.
–Crane for equipment handlingCrane for equipment handling
–HelipadHelipad
PLATFORM PARTSPLATFORM PARTS
TOPSIDE:TOPSIDE:
–Facilities are tailored to achieve Facilities are tailored to achieve
weight and space savingweight and space saving
–Incorporates process and utility Incorporates process and utility
equipment equipment
Drilling RigDrilling Rig
Injection CompressorsInjection Compressors
Gas CompressorsGas Compressors
Gas Turbine GeneratorsGas Turbine Generators
PipingPiping
HVACHVAC
InstrumentationInstrumentation
–Accommodation for operating Accommodation for operating
personnel.personnel.
–Crane for equipment handlingCrane for equipment handling
–HelipadHelipad
OFFSHORE PLATFORM DESIGN07/30/2003
PLATFORM PARTSPLATFORM PARTS
MOORINGS & ANCHORS:MOORINGS & ANCHORS:
–Used to tie platform in place Used to tie platform in place
–MaterialMaterial
Steel chainSteel chain
Steel wire rope Steel wire rope
–Catenary shape due to heavy Catenary shape due to heavy
weight. weight.
–Length of rope is moreLength of rope is more
Synthetic fiber ropeSynthetic fiber rope
–Taut shape due to substantial Taut shape due to substantial
less weight than steel ropes.less weight than steel ropes.
–Less rope length requiredLess rope length required
–Corrosion freeCorrosion free
PLATFORM PARTSPLATFORM PARTS
MOORINGS & ANCHORS:MOORINGS & ANCHORS:
–Used to tie platform in place Used to tie platform in place
–MaterialMaterial
Steel chainSteel chain
Steel wire rope Steel wire rope
–Catenary shape due to heavy Catenary shape due to heavy
weight. weight.
–Length of rope is moreLength of rope is more
Synthetic fiber ropeSynthetic fiber rope
–Taut shape due to substantial Taut shape due to substantial
less weight than steel ropes.less weight than steel ropes.
–Less rope length requiredLess rope length required
–Corrosion freeCorrosion free
OFFSHORE PLATFORM DESIGN07/30/2003
PLATFORM PARTSPLATFORM PARTS
RISER:RISER:
–Pipes used for production, drilling, Pipes used for production, drilling,
and export of Oil and Gas from and export of Oil and Gas from
Seabed.Seabed.
–Riser system is a key component Riser system is a key component
for offshore drilling or floating for offshore drilling or floating
production projects.production projects.
–The cost and technical challenges The cost and technical challenges
of the riser system increase of the riser system increase
significantly with water depth.significantly with water depth.
–Design of riser system depends on Design of riser system depends on
filed layout, vessel interfaces, filed layout, vessel interfaces,
fluid properties and environmental fluid properties and environmental
condition.condition.
PLATFORM PARTSPLATFORM PARTS
RISER:RISER:
–Pipes used for production, drilling, Pipes used for production, drilling,
and export of Oil and Gas from and export of Oil and Gas from
Seabed.Seabed.
–Riser system is a key component Riser system is a key component
for offshore drilling or floating for offshore drilling or floating
production projects.production projects.
–The cost and technical challenges The cost and technical challenges
of the riser system increase of the riser system increase
significantly with water depth.significantly with water depth.
–Design of riser system depends on Design of riser system depends on
filed layout, vessel interfaces, filed layout, vessel interfaces,
fluid properties and environmental fluid properties and environmental
condition.condition.
OFFSHORE PLATFORM DESIGN07/30/2003
PLATFORM PARTSPLATFORM PARTS
RISER:RISER:
–Remains in tension due to self Remains in tension due to self
weightweight
–Profiles are designed to reduce Profiles are designed to reduce
load on topside. Types of risersload on topside. Types of risers
RigidRigid
Flexible - Allows vessel motion Flexible - Allows vessel motion
due to wave loading and due to wave loading and
compensates heave motioncompensates heave motion
–Simple Catenary risers: Simple Catenary risers:
Flexible pipe is freely Flexible pipe is freely
suspended between surface suspended between surface
vessel and the seabed.vessel and the seabed.
–Other catenary variants Other catenary variants
possiblepossible
PLATFORM PARTSPLATFORM PARTS
RISER:RISER:
–Remains in tension due to self Remains in tension due to self
weightweight
–Profiles are designed to reduce Profiles are designed to reduce
load on topside. Types of risersload on topside. Types of risers
RigidRigid
Flexible - Allows vessel motion Flexible - Allows vessel motion
due to wave loading and due to wave loading and
compensates heave motioncompensates heave motion
–Simple Catenary risers: Simple Catenary risers:
Flexible pipe is freely Flexible pipe is freely
suspended between surface suspended between surface
vessel and the seabed.vessel and the seabed.
–Other catenary variants Other catenary variants
possiblepossible
OFFSHORE PLATFORM DESIGN07/30/2003
PLATFORM PLATFORM
INSTALLATIONINSTALLATION
BARGE LOADOUT:BARGE LOADOUT:
–Various methods are deployed based Various methods are deployed based
on availability of resources and size of on availability of resources and size of
structure.structure.
Barge CraneBarge Crane
Flat over - Top side is installed on Flat over - Top side is installed on
jackets. Ballasting of bargejackets. Ballasting of barge
Smaller jackets can be installed Smaller jackets can be installed
by lifting them off barge using a by lifting them off barge using a
floating vessel with cranesfloating vessel with cranes..
–Large 400’ x 100’ deck barges capable Large 400’ x 100’ deck barges capable
of carrying up to 12,000 tons are of carrying up to 12,000 tons are
availableavailable
PLATFORM PLATFORM
INSTALLATIONINSTALLATION
BARGE LOADOUT:BARGE LOADOUT:
–Various methods are deployed based Various methods are deployed based
on availability of resources and size of on availability of resources and size of
structure.structure.
Barge CraneBarge Crane
Flat over - Top side is installed on Flat over - Top side is installed on
jackets. Ballasting of bargejackets. Ballasting of barge
Smaller jackets can be installed Smaller jackets can be installed
by lifting them off barge using a by lifting them off barge using a
floating vessel with cranesfloating vessel with cranes..
–Large 400’ x 100’ deck barges capable Large 400’ x 100’ deck barges capable
of carrying up to 12,000 tons are of carrying up to 12,000 tons are
availableavailable
OFFSHORE PLATFORM DESIGN07/30/2003
CORROSION PROTECTIONCORROSION PROTECTION
The usual form of corrosion protection
of the underwater part of the jacket as
well as the upper part of the piles in
soil is by cathodic protection using
sacrificial anodes.
A sacrificial anode consists of a
zinc/aluminium bar cast about a steel
tube and welded on to the structures.
Typically approximately 5% of the
jacket weight is applied as anodes.
The steelwork in the splash zone is
usually protected by a sacrificial wall
thickness of 12 mm to the members.
CORROSION PROTECTIONCORROSION PROTECTION
The usual form of corrosion protection
of the underwater part of the jacket as
well as the upper part of the piles in
soil is by cathodic protection using
sacrificial anodes.
A sacrificial anode consists of a
zinc/aluminium bar cast about a steel
tube and welded on to the structures.
Typically approximately 5% of the
jacket weight is applied as anodes.
The steelwork in the splash zone is
usually protected by a sacrificial wall
thickness of 12 mm to the members.
OFFSHORE PLATFORM DESIGN07/30/2003
PLATFORM PLATFORM
FOUNDATIONFOUNDATION
FOUNDATION:FOUNDATION:
–The loads generated by environmental The loads generated by environmental
conditions plus by onboard equipment conditions plus by onboard equipment
must be resisted by the piles at the must be resisted by the piles at the
seabed and below.seabed and below.
–The soil investigation is vital to the The soil investigation is vital to the
design of any offshore structure. design of any offshore structure.
Geotech report is developed by doing Geotech report is developed by doing
soil borings at the desired location, soil borings at the desired location,
and performing in-situ and laboratory and performing in-situ and laboratory
tests.tests.
–Pile penetrations depends on platform Pile penetrations depends on platform
size and loads, and soil characteristics, size and loads, and soil characteristics,
but normally range from 30 meters to but normally range from 30 meters to
about 100 meters. about 100 meters.
PLATFORM PLATFORM
FOUNDATIONFOUNDATION
FOUNDATION:FOUNDATION:
–The loads generated by environmental The loads generated by environmental
conditions plus by onboard equipment conditions plus by onboard equipment
must be resisted by the piles at the must be resisted by the piles at the
seabed and below.seabed and below.
–The soil investigation is vital to the The soil investigation is vital to the
design of any offshore structure. design of any offshore structure.
Geotech report is developed by doing Geotech report is developed by doing
soil borings at the desired location, soil borings at the desired location,
and performing in-situ and laboratory and performing in-situ and laboratory
tests.tests.
–Pile penetrations depends on platform Pile penetrations depends on platform
size and loads, and soil characteristics, size and loads, and soil characteristics,
but normally range from 30 meters to but normally range from 30 meters to
about 100 meters. about 100 meters.
OFFSHORE PLATFORM DESIGN07/30/2003
NAVAL ARCHITECTURENAVAL ARCHITECTURE
HYDROSTATICS AND STABILITY:HYDROSTATICS AND STABILITY:
–Stability is resistance to capsizingStability is resistance to capsizing
–Center of Buoyancy is located at center of Center of Buoyancy is located at center of
mass of the displaced water.mass of the displaced water.
–Under no external forces, the center of Under no external forces, the center of
gravity and center of buoyancy are in gravity and center of buoyancy are in
same vertical plane.same vertical plane.
–Upward force of water equals to the Upward force of water equals to the
weight of floating vessel and this weight weight of floating vessel and this weight
is equal to weight of displaced wateris equal to weight of displaced water
–Under wind load vessel heels, and thus Under wind load vessel heels, and thus
CoB moves to provide righting CoB moves to provide righting
(stabilizing) moment.(stabilizing) moment.
–Vertical line through new center of Vertical line through new center of
buoyancy will intersect CoG at point M buoyancy will intersect CoG at point M
called as Metacentercalled as Metacenter
NAVAL ARCHITECTURENAVAL ARCHITECTURE
HYDROSTATICS AND STABILITY:HYDROSTATICS AND STABILITY:
–Stability is resistance to capsizingStability is resistance to capsizing
–Center of Buoyancy is located at center of Center of Buoyancy is located at center of
mass of the displaced water.mass of the displaced water.
–Under no external forces, the center of Under no external forces, the center of
gravity and center of buoyancy are in gravity and center of buoyancy are in
same vertical plane.same vertical plane.
–Upward force of water equals to the Upward force of water equals to the
weight of floating vessel and this weight weight of floating vessel and this weight
is equal to weight of displaced wateris equal to weight of displaced water
–Under wind load vessel heels, and thus Under wind load vessel heels, and thus
CoB moves to provide righting CoB moves to provide righting
(stabilizing) moment.(stabilizing) moment.
–Vertical line through new center of Vertical line through new center of
buoyancy will intersect CoG at point M buoyancy will intersect CoG at point M
called as Metacentercalled as Metacenter
OFFSHORE PLATFORM DESIGN07/30/2003
NAVAL ARCHITECTURENAVAL ARCHITECTURE
HYDROSTATICS AND HYDROSTATICS AND
STABILITY:STABILITY:
–Intact stabilityIntact stability requires righting requires righting
moment adequate to withstand moment adequate to withstand
wind moments. wind moments.
–Damage stabilityDamage stability requires vessel requires vessel
withstands flooding of withstands flooding of
designated volume with wind designated volume with wind
moments. moments.
–CoG of partially filled vessel CoG of partially filled vessel
changes, due to heeling. This changes, due to heeling. This
results in reduction in stability. results in reduction in stability.
This phenomena is called Free This phenomena is called Free
surface correction (FSC).surface correction (FSC).
HYDRODYNAMIC RESPONSE:
Rigid body response
There are six rigid body motions:
•Translational - Surge, sway and heave
•Rotational - Roll, pitch and yaw
Structural response - Involving structural deformations
NAVAL ARCHITECTURENAVAL ARCHITECTURE
HYDROSTATICS AND HYDROSTATICS AND
STABILITY:STABILITY:
–Intact stabilityIntact stability requires righting requires righting
moment adequate to withstand moment adequate to withstand
wind moments. wind moments.
–Damage stabilityDamage stability requires vessel requires vessel
withstands flooding of withstands flooding of
designated volume with wind designated volume with wind
moments. moments.
–CoG of partially filled vessel CoG of partially filled vessel
changes, due to heeling. This changes, due to heeling. This
results in reduction in stability. results in reduction in stability.
This phenomena is called Free This phenomena is called Free
surface correction (FSC).surface correction (FSC).
HYDRODYNAMIC RESPONSE:
Rigid body response
There are six rigid body motions:
•Translational - Surge, sway and heave
•Rotational - Roll, pitch and yaw
Structural response - Involving structural deformations
07/30/2003 OFFSHORE
PLATFORM DESIGN
STRUCTURAL DESIGNSTRUCTURAL DESIGN
Loads:Loads:
Offshore structure shall be designed for Offshore structure shall be designed for
following types of loads: following types of loads:
–Permanent (dead) loads. Permanent (dead) loads.
–Operating (live) loads. Operating (live) loads.
–Environmental loads Environmental loads
Wind loadWind load
Wave loadWave load
Earthquake loadEarthquake load
–Construction - installation loads. Construction - installation loads.
–Accidental loads.Accidental loads.
The design of offshore structures is The design of offshore structures is
dominated by environmental loads, dominated by environmental loads,
especially wave loadespecially wave load
PLATFORM DESIGN
STRUCTURAL DESIGNSTRUCTURAL DESIGN
Loads:Loads:
Offshore structure shall be designed for Offshore structure shall be designed for
following types of loads: following types of loads:
–Permanent (dead) loads. Permanent (dead) loads.
–Operating (live) loads. Operating (live) loads.
–Environmental loads Environmental loads
Wind loadWind load
Wave loadWave load
Earthquake loadEarthquake load
–Construction - installation loads. Construction - installation loads.
–Accidental loads.Accidental loads.
The design of offshore structures is The design of offshore structures is
dominated by environmental loads, dominated by environmental loads,
especially wave loadespecially wave load
07/30/2003 OFFSHORE
PLATFORM DESIGN
STRUCTURAL DESIGNSTRUCTURAL DESIGN
Permanent Loads:Permanent Loads:
Weight of the structure in air, Weight of the structure in air,
including the weight of ballast.including the weight of ballast.
–Weights of equipment, and Weights of equipment, and
associated structures permanently associated structures permanently
mounted on the platform.mounted on the platform.
–Hydrostatic forces on the members Hydrostatic forces on the members
below the waterline. These forces below the waterline. These forces
include buoyancy and hydrostatic include buoyancy and hydrostatic
pressures.pressures.
PLATFORM DESIGN
STRUCTURAL DESIGNSTRUCTURAL DESIGN
Permanent Loads:Permanent Loads:
Weight of the structure in air, Weight of the structure in air,
including the weight of ballast.including the weight of ballast.
–Weights of equipment, and Weights of equipment, and
associated structures permanently associated structures permanently
mounted on the platform.mounted on the platform.
–Hydrostatic forces on the members Hydrostatic forces on the members
below the waterline. These forces below the waterline. These forces
include buoyancy and hydrostatic include buoyancy and hydrostatic
pressures.pressures.
07/30/2003 OFFSHORE
PLATFORM DESIGN
STRUCTURAL DESIGNSTRUCTURAL DESIGN
Operating (Live) Loads:Operating (Live) Loads:
–Operating loads include the weight of all non-Operating loads include the weight of all non-
permanent equipment or material, as well as forces permanent equipment or material, as well as forces
generated during operation of equipment. generated during operation of equipment.
The weight of drilling, production facilities, The weight of drilling, production facilities,
living quarters, furniture, life support systems, living quarters, furniture, life support systems,
heliport, consumable supplies, liquids, etc.heliport, consumable supplies, liquids, etc.
Forces generated during operations, e.g. drilling, Forces generated during operations, e.g. drilling,
vessel mooring, helicopter landing, crane vessel mooring, helicopter landing, crane
operations.operations.
Following Live load values are recommended in Following Live load values are recommended in
BS6235:BS6235:
Crew quarters and passage ways: 3.2 KN/mCrew quarters and passage ways: 3.2 KN/m
22
Working areas: 8,5 KN/mWorking areas: 8,5 KN/m
22
PLATFORM DESIGN
STRUCTURAL DESIGNSTRUCTURAL DESIGN
Operating (Live) Loads:Operating (Live) Loads:
–Operating loads include the weight of all non-Operating loads include the weight of all non-
permanent equipment or material, as well as forces permanent equipment or material, as well as forces
generated during operation of equipment. generated during operation of equipment.
The weight of drilling, production facilities, The weight of drilling, production facilities,
living quarters, furniture, life support systems, living quarters, furniture, life support systems,
heliport, consumable supplies, liquids, etc.heliport, consumable supplies, liquids, etc.
Forces generated during operations, e.g. drilling, Forces generated during operations, e.g. drilling,
vessel mooring, helicopter landing, crane vessel mooring, helicopter landing, crane
operations.operations.
Following Live load values are recommended in Following Live load values are recommended in
BS6235:BS6235:
Crew quarters and passage ways: 3.2 KN/mCrew quarters and passage ways: 3.2 KN/m
22
Working areas: 8,5 KN/mWorking areas: 8,5 KN/m
22
07/30/2003 OFFSHORE
PLATFORM DESIGN
STRUCTURAL DESIGNSTRUCTURAL DESIGN
Wind Loads:Wind Loads:
Wind load act on portion of platform above Wind load act on portion of platform above
the water level as well as on any equipment, the water level as well as on any equipment,
housing, derrick, etc.housing, derrick, etc.
For combination with wave loads, codes For combination with wave loads, codes
recommend the most unfavorable of the recommend the most unfavorable of the
following two loadings:following two loadings:
–1 minute sustained wind speeds 1 minute sustained wind speeds
combined with extreme waves.combined with extreme waves.
–3 second gusts3 second gusts..
When, the ratio of height to the least When, the ratio of height to the least
horizontal dimension of structure is greater horizontal dimension of structure is greater
than 5, then API-RP2A requires the dynamic than 5, then API-RP2A requires the dynamic
effects of the wind to be taken into account effects of the wind to be taken into account
and the flow induced cyclic wind loads due to and the flow induced cyclic wind loads due to
vortex shedding must be investigated.vortex shedding must be investigated.
PLATFORM DESIGN
STRUCTURAL DESIGNSTRUCTURAL DESIGN
Wind Loads:Wind Loads:
Wind load act on portion of platform above Wind load act on portion of platform above
the water level as well as on any equipment, the water level as well as on any equipment,
housing, derrick, etc.housing, derrick, etc.
For combination with wave loads, codes For combination with wave loads, codes
recommend the most unfavorable of the recommend the most unfavorable of the
following two loadings:following two loadings:
–1 minute sustained wind speeds 1 minute sustained wind speeds
combined with extreme waves.combined with extreme waves.
–3 second gusts3 second gusts..
When, the ratio of height to the least When, the ratio of height to the least
horizontal dimension of structure is greater horizontal dimension of structure is greater
than 5, then API-RP2A requires the dynamic than 5, then API-RP2A requires the dynamic
effects of the wind to be taken into account effects of the wind to be taken into account
and the flow induced cyclic wind loads due to and the flow induced cyclic wind loads due to
vortex shedding must be investigated.vortex shedding must be investigated.
07/30/2003 OFFSHORE
PLATFORM DESIGN
STRUCTURAL DESIGNSTRUCTURAL DESIGN
Wave loadWave load::
The wave loading of an offshore structure is usually the most important of all environmental The wave loading of an offshore structure is usually the most important of all environmental
loadings.loadings.
The forces on the structure are caused by the motion of the water due to the waves The forces on the structure are caused by the motion of the water due to the waves
Determination of wave forces requires the solution of ,Determination of wave forces requires the solution of ,
a) Sea state using an idealization of the wave surface profile and the wave kinematics by wave a) Sea state using an idealization of the wave surface profile and the wave kinematics by wave
theory. theory.
b) Computation of the wave forces on individual members and on the total structure, from the b) Computation of the wave forces on individual members and on the total structure, from the
fluid motion.fluid motion.
Design wave concept is used, where a regular wave of given height and period is defined and Design wave concept is used, where a regular wave of given height and period is defined and
the forces due to this wave are calculated using a high-order wave theory. Usually the the forces due to this wave are calculated using a high-order wave theory. Usually the
maximum wave with a return period of 100 years, is chosen. No dynamic behavior of the maximum wave with a return period of 100 years, is chosen. No dynamic behavior of the
structure is considered. This static analysis is appropriate when the dominant wave periods are structure is considered. This static analysis is appropriate when the dominant wave periods are
well above the period of the structure. This is the case of extreme storm waves acting on well above the period of the structure. This is the case of extreme storm waves acting on
shallow water structures. shallow water structures.
PLATFORM DESIGN
STRUCTURAL DESIGNSTRUCTURAL DESIGN
Wave loadWave load::
The wave loading of an offshore structure is usually the most important of all environmental The wave loading of an offshore structure is usually the most important of all environmental
loadings.loadings.
The forces on the structure are caused by the motion of the water due to the waves The forces on the structure are caused by the motion of the water due to the waves
Determination of wave forces requires the solution of ,Determination of wave forces requires the solution of ,
a) Sea state using an idealization of the wave surface profile and the wave kinematics by wave a) Sea state using an idealization of the wave surface profile and the wave kinematics by wave
theory. theory.
b) Computation of the wave forces on individual members and on the total structure, from the b) Computation of the wave forces on individual members and on the total structure, from the
fluid motion.fluid motion.
Design wave concept is used, where a regular wave of given height and period is defined and Design wave concept is used, where a regular wave of given height and period is defined and
the forces due to this wave are calculated using a high-order wave theory. Usually the the forces due to this wave are calculated using a high-order wave theory. Usually the
maximum wave with a return period of 100 years, is chosen. No dynamic behavior of the maximum wave with a return period of 100 years, is chosen. No dynamic behavior of the
structure is considered. This static analysis is appropriate when the dominant wave periods are structure is considered. This static analysis is appropriate when the dominant wave periods are
well above the period of the structure. This is the case of extreme storm waves acting on well above the period of the structure. This is the case of extreme storm waves acting on
shallow water structures. shallow water structures.
07/30/2003 OFFSHORE
PLATFORM DESIGN
STRUCTURAL DESIGNSTRUCTURAL DESIGN
Wave Load: (Contd.)
•Wave theoriesWave theories
Wave theories describe the kinematics of waves of water. They serve to calculate the particle Wave theories describe the kinematics of waves of water. They serve to calculate the particle
velocities and accelerations and the dynamic pressure as functions of the surface elevation of velocities and accelerations and the dynamic pressure as functions of the surface elevation of
the waves. The waves are assumed to be long-crested, i.e. they can be described by a two-the waves. The waves are assumed to be long-crested, i.e. they can be described by a two-
dimensional flow field, and are characterized by the parameters: wave height (H), period (T) dimensional flow field, and are characterized by the parameters: wave height (H), period (T)
and water depth (d).and water depth (d).
PLATFORM DESIGN
STRUCTURAL DESIGNSTRUCTURAL DESIGN
Wave Load: (Contd.)
•Wave theoriesWave theories
Wave theories describe the kinematics of waves of water. They serve to calculate the particle Wave theories describe the kinematics of waves of water. They serve to calculate the particle
velocities and accelerations and the dynamic pressure as functions of the surface elevation of velocities and accelerations and the dynamic pressure as functions of the surface elevation of
the waves. The waves are assumed to be long-crested, i.e. they can be described by a two-the waves. The waves are assumed to be long-crested, i.e. they can be described by a two-
dimensional flow field, and are characterized by the parameters: wave height (H), period (T) dimensional flow field, and are characterized by the parameters: wave height (H), period (T)
and water depth (d).and water depth (d).
07/30/2003 OFFSHORE
PLATFORM DESIGN
STRUCTURAL DESIGNSTRUCTURAL DESIGN
Wave theories: Wave theories: (Contd.)(Contd.)
•Wave forces on structural membersWave forces on structural members
Structures exposed to waves experience forces much higher than wind loadings. The forces Structures exposed to waves experience forces much higher than wind loadings. The forces
result from the dynamic pressure and the water particle motions. Two different cases can be result from the dynamic pressure and the water particle motions. Two different cases can be
distinguished:distinguished:
Large volume bodies, termed hydrodynamic compact structures, influence the wave field by Large volume bodies, termed hydrodynamic compact structures, influence the wave field by
diffraction and reflection. The forces on these bodies have to be determined by calculations diffraction and reflection. The forces on these bodies have to be determined by calculations
based on diffraction theory. based on diffraction theory.
Slender, hydro-dynamically transparent structures have no significant influence on the wave Slender, hydro-dynamically transparent structures have no significant influence on the wave
field. The forces can be calculated in a straight-forward manner with Morison's equation. The field. The forces can be calculated in a straight-forward manner with Morison's equation. The
steel jackets of offshore structures can usually be regarded as hydro-dynamically transparentsteel jackets of offshore structures can usually be regarded as hydro-dynamically transparent
As a rule, Morison's equation may be applied when D/L < 0.2, where D is the member As a rule, Morison's equation may be applied when D/L < 0.2, where D is the member
diameter and L is the wave length.diameter and L is the wave length.
Morison's equation expresses the wave force as the sum of,Morison's equation expresses the wave force as the sum of,
–
An inertia force proportional to the particle acceleration An inertia force proportional to the particle acceleration
–
A non-linear drag force proportional to the square of the particle velocity.A non-linear drag force proportional to the square of the particle velocity.
PLATFORM DESIGN
STRUCTURAL DESIGNSTRUCTURAL DESIGN
Wave theories: Wave theories: (Contd.)(Contd.)
•Wave forces on structural membersWave forces on structural members
Structures exposed to waves experience forces much higher than wind loadings. The forces Structures exposed to waves experience forces much higher than wind loadings. The forces
result from the dynamic pressure and the water particle motions. Two different cases can be result from the dynamic pressure and the water particle motions. Two different cases can be
distinguished:distinguished:
Large volume bodies, termed hydrodynamic compact structures, influence the wave field by Large volume bodies, termed hydrodynamic compact structures, influence the wave field by
diffraction and reflection. The forces on these bodies have to be determined by calculations diffraction and reflection. The forces on these bodies have to be determined by calculations
based on diffraction theory. based on diffraction theory.
Slender, hydro-dynamically transparent structures have no significant influence on the wave Slender, hydro-dynamically transparent structures have no significant influence on the wave
field. The forces can be calculated in a straight-forward manner with Morison's equation. The field. The forces can be calculated in a straight-forward manner with Morison's equation. The
steel jackets of offshore structures can usually be regarded as hydro-dynamically transparentsteel jackets of offshore structures can usually be regarded as hydro-dynamically transparent
As a rule, Morison's equation may be applied when D/L < 0.2, where D is the member As a rule, Morison's equation may be applied when D/L < 0.2, where D is the member
diameter and L is the wave length.diameter and L is the wave length.
Morison's equation expresses the wave force as the sum of,Morison's equation expresses the wave force as the sum of,
–
An inertia force proportional to the particle acceleration An inertia force proportional to the particle acceleration
–
A non-linear drag force proportional to the square of the particle velocity.A non-linear drag force proportional to the square of the particle velocity.
07/30/2003 OFFSHORE
PLATFORM DESIGN
STRUCTURAL DESIGNSTRUCTURAL DESIGN
Earthquake load: Earthquake load:
Offshore structures are designed for Offshore structures are designed for
two levels of earthquake intensity.two levels of earthquake intensity.
Strength level :Earthquake, Strength level :Earthquake,
defined as having a "reasonable defined as having a "reasonable
likelihood of not being exceeded likelihood of not being exceeded
during the platform's life" (mean during the platform's life" (mean
recurrence interval ~ 200 - 500 recurrence interval ~ 200 - 500
years), the structure is designed years), the structure is designed
to respond elastically. to respond elastically.
Ductility level : Earthquake, Ductility level : Earthquake,
defined as close to the defined as close to the
"maximum credible earthquake" "maximum credible earthquake"
at the site, the structure is at the site, the structure is
designed for inelastic response designed for inelastic response
and to have adequate reserve and to have adequate reserve
strength to avoid collapse.strength to avoid collapse.
PLATFORM DESIGN
STRUCTURAL DESIGNSTRUCTURAL DESIGN
Earthquake load: Earthquake load:
Offshore structures are designed for Offshore structures are designed for
two levels of earthquake intensity.two levels of earthquake intensity.
Strength level :Earthquake, Strength level :Earthquake,
defined as having a "reasonable defined as having a "reasonable
likelihood of not being exceeded likelihood of not being exceeded
during the platform's life" (mean during the platform's life" (mean
recurrence interval ~ 200 - 500 recurrence interval ~ 200 - 500
years), the structure is designed years), the structure is designed
to respond elastically. to respond elastically.
Ductility level : Earthquake, Ductility level : Earthquake,
defined as close to the defined as close to the
"maximum credible earthquake" "maximum credible earthquake"
at the site, the structure is at the site, the structure is
designed for inelastic response designed for inelastic response
and to have adequate reserve and to have adequate reserve
strength to avoid collapse.strength to avoid collapse.
07/30/2003 OFFSHORE
PLATFORM DESIGN
STRUCTURAL DESIGNSTRUCTURAL DESIGN
Ice and Snow Loads:Ice and Snow Loads:
Ice is a primary problem for marine structures in the arctic and sub-arctic zones. Ice Ice is a primary problem for marine structures in the arctic and sub-arctic zones. Ice
formation and expansion can generate large pressures that give rise to horizontal as well as formation and expansion can generate large pressures that give rise to horizontal as well as
vertical forces. In addition, large blocks of ice driven by current, winds and waves with vertical forces. In addition, large blocks of ice driven by current, winds and waves with
speeds up to 0,5 to 1,0 m/s, may hit the structure and produce impact loads.speeds up to 0,5 to 1,0 m/s, may hit the structure and produce impact loads.
Temperature Load:Temperature Load:
Temperature gradients produce thermal stresses. To cater such stresses, extreme values of Temperature gradients produce thermal stresses. To cater such stresses, extreme values of
sea and air temperatures which are likely to occur during the life of the structure shall be sea and air temperatures which are likely to occur during the life of the structure shall be
estimated. In addition to the environmental sources , accidental release of cryogenic estimated. In addition to the environmental sources , accidental release of cryogenic
material can result in temperature increase, which must be taken into account as accidental material can result in temperature increase, which must be taken into account as accidental
loads. The temperature of the oil and gas produced must also be considered.loads. The temperature of the oil and gas produced must also be considered.
Marine Growth:Marine Growth:
Marine growth is accumulated on submerged members. Its main effect is to increase the
wave forces on the members by increasing exposed areas and drag coefficient due to higher
surface roughness. It is accounted for in design through appropriate increases in the
diameters and masses of the submerged members.
PLATFORM DESIGN
STRUCTURAL DESIGNSTRUCTURAL DESIGN
Ice and Snow Loads:Ice and Snow Loads:
Ice is a primary problem for marine structures in the arctic and sub-arctic zones. Ice Ice is a primary problem for marine structures in the arctic and sub-arctic zones. Ice
formation and expansion can generate large pressures that give rise to horizontal as well as formation and expansion can generate large pressures that give rise to horizontal as well as
vertical forces. In addition, large blocks of ice driven by current, winds and waves with vertical forces. In addition, large blocks of ice driven by current, winds and waves with
speeds up to 0,5 to 1,0 m/s, may hit the structure and produce impact loads.speeds up to 0,5 to 1,0 m/s, may hit the structure and produce impact loads.
Temperature Load:Temperature Load:
Temperature gradients produce thermal stresses. To cater such stresses, extreme values of Temperature gradients produce thermal stresses. To cater such stresses, extreme values of
sea and air temperatures which are likely to occur during the life of the structure shall be sea and air temperatures which are likely to occur during the life of the structure shall be
estimated. In addition to the environmental sources , accidental release of cryogenic estimated. In addition to the environmental sources , accidental release of cryogenic
material can result in temperature increase, which must be taken into account as accidental material can result in temperature increase, which must be taken into account as accidental
loads. The temperature of the oil and gas produced must also be considered.loads. The temperature of the oil and gas produced must also be considered.
Marine Growth:Marine Growth:
Marine growth is accumulated on submerged members. Its main effect is to increase the
wave forces on the members by increasing exposed areas and drag coefficient due to higher
surface roughness. It is accounted for in design through appropriate increases in the
diameters and masses of the submerged members.
07/30/2003 OFFSHORE
PLATFORM DESIGN
STRUCTURAL DESIGNSTRUCTURAL DESIGN
Installation Load :Installation Load :
These are temporary loads and arise during These are temporary loads and arise during
fabrication and installation of the platform or fabrication and installation of the platform or
its components. During fabrication, erection its components. During fabrication, erection
lifts of various structural components lifts of various structural components
generate lifting forces, while in the generate lifting forces, while in the
installation phase forces are generated during installation phase forces are generated during
platform load out, transportation to the site, platform load out, transportation to the site,
launching and upending, as well as during launching and upending, as well as during
lifts related to installation.lifts related to installation.
All members and connections of a lifted All members and connections of a lifted
component must be designed for the forces component must be designed for the forces
resulting from static equilibrium of the lifted resulting from static equilibrium of the lifted
weight and the sling tensions.weight and the sling tensions.
Load out forces are generated when the jacket Load out forces are generated when the jacket
is loaded from the fabrication yard onto the is loaded from the fabrication yard onto the
barge. Depends on friction co-efficientbarge. Depends on friction co-efficient
PLATFORM DESIGN
STRUCTURAL DESIGNSTRUCTURAL DESIGN
Installation Load :Installation Load :
These are temporary loads and arise during These are temporary loads and arise during
fabrication and installation of the platform or fabrication and installation of the platform or
its components. During fabrication, erection its components. During fabrication, erection
lifts of various structural components lifts of various structural components
generate lifting forces, while in the generate lifting forces, while in the
installation phase forces are generated during installation phase forces are generated during
platform load out, transportation to the site, platform load out, transportation to the site,
launching and upending, as well as during launching and upending, as well as during
lifts related to installation.lifts related to installation.
All members and connections of a lifted All members and connections of a lifted
component must be designed for the forces component must be designed for the forces
resulting from static equilibrium of the lifted resulting from static equilibrium of the lifted
weight and the sling tensions.weight and the sling tensions.
Load out forces are generated when the jacket Load out forces are generated when the jacket
is loaded from the fabrication yard onto the is loaded from the fabrication yard onto the
barge. Depends on friction co-efficientbarge. Depends on friction co-efficient
07/30/2003 OFFSHORE
PLATFORM DESIGN
STRUCTURAL DESIGNSTRUCTURAL DESIGN
Accidental LoadAccidental Load : :
According to the DNV rules , accidental According to the DNV rules , accidental
loads are loads, which may occur as a result loads are loads, which may occur as a result
of accident or exceptional circumstances. of accident or exceptional circumstances.
Examples of accidental loads are, collision Examples of accidental loads are, collision
with vessels, fire or explosion, dropped with vessels, fire or explosion, dropped
objects, and unintended flooding of objects, and unintended flooding of
buoyancy tanks. buoyancy tanks.
Special measures are normally taken to Special measures are normally taken to
reduce the risk from accidental loads.reduce the risk from accidental loads.
PLATFORM DESIGN
STRUCTURAL DESIGNSTRUCTURAL DESIGN
Accidental LoadAccidental Load : :
According to the DNV rules , accidental According to the DNV rules , accidental
loads are loads, which may occur as a result loads are loads, which may occur as a result
of accident or exceptional circumstances. of accident or exceptional circumstances.
Examples of accidental loads are, collision Examples of accidental loads are, collision
with vessels, fire or explosion, dropped with vessels, fire or explosion, dropped
objects, and unintended flooding of objects, and unintended flooding of
buoyancy tanks. buoyancy tanks.
Special measures are normally taken to Special measures are normally taken to
reduce the risk from accidental loads.reduce the risk from accidental loads.
07/30/2003 OFFSHORE
PLATFORM DESIGN
STRUCTURAL DESIGNSTRUCTURAL DESIGN
Load CombinationsLoad Combinations : :
The load combinations depend upon the design method used, i.e. whether limit
state or allowable stress design is employed.
The load combinations recommended for use with allowable stress procedures are:
Normal operations
Dead loads plus operating environmental loads plus maximum live loads.
Dead loads plus operating environmental loads plus minimum live loads.
Extreme operations
Dead loads plus extreme environmental loads plus maximum live loads.
Dead loads plus extreme environmental loads plus minimum live loads
Environmental loads,should be combined in a manner consistent with their joint
probability of occurrence.
Earthquake loads, are to be imposed as a separate environmental load, i.e., not to
be combined with waves, wind, etc.
PLATFORM DESIGN
STRUCTURAL DESIGNSTRUCTURAL DESIGN
Load CombinationsLoad Combinations : :
The load combinations depend upon the design method used, i.e. whether limit
state or allowable stress design is employed.
The load combinations recommended for use with allowable stress procedures are:
Normal operations
Dead loads plus operating environmental loads plus maximum live loads.
Dead loads plus operating environmental loads plus minimum live loads.
Extreme operations
Dead loads plus extreme environmental loads plus maximum live loads.
Dead loads plus extreme environmental loads plus minimum live loads
Environmental loads,should be combined in a manner consistent with their joint
probability of occurrence.
Earthquake loads, are to be imposed as a separate environmental load, i.e., not to
be combined with waves, wind, etc.
OFFSHORE PLATFORM DESIGN07/30/2003
STRUCTURAL ANALYSISSTRUCTURAL ANALYSIS
ANALYSIS MODEL:ANALYSIS MODEL:
The analytical models used in offshore The analytical models used in offshore
engineering are similar to other types of on engineering are similar to other types of on
shore steel structuresshore steel structures
The same model is used throughout the The same model is used throughout the
analysis except supports locations.analysis except supports locations.
Stick models are used extensively for Stick models are used extensively for
tubular structures (jackets, bridges, flare tubular structures (jackets, bridges, flare
booms) and lattice trusses (modules, booms) and lattice trusses (modules,
decks).decks).
Each member is normally rigidly fixed at Each member is normally rigidly fixed at
its ends to other elements in the model.its ends to other elements in the model.
In addition to its geometrical and material In addition to its geometrical and material
properties, each member is characterized by properties, each member is characterized by
hydrodynamic coefficients, e.g. relating to hydrodynamic coefficients, e.g. relating to
drag, inertia, and marine growth, to allow drag, inertia, and marine growth, to allow
wave forces to be automatically generated.wave forces to be automatically generated.
STRUCTURAL ANALYSISSTRUCTURAL ANALYSIS
ANALYSIS MODEL:ANALYSIS MODEL:
The analytical models used in offshore The analytical models used in offshore
engineering are similar to other types of on engineering are similar to other types of on
shore steel structuresshore steel structures
The same model is used throughout the The same model is used throughout the
analysis except supports locations.analysis except supports locations.
Stick models are used extensively for Stick models are used extensively for
tubular structures (jackets, bridges, flare tubular structures (jackets, bridges, flare
booms) and lattice trusses (modules, booms) and lattice trusses (modules,
decks).decks).
Each member is normally rigidly fixed at Each member is normally rigidly fixed at
its ends to other elements in the model.its ends to other elements in the model.
In addition to its geometrical and material In addition to its geometrical and material
properties, each member is characterized by properties, each member is characterized by
hydrodynamic coefficients, e.g. relating to hydrodynamic coefficients, e.g. relating to
drag, inertia, and marine growth, to allow drag, inertia, and marine growth, to allow
wave forces to be automatically generated.wave forces to be automatically generated.
OFFSHORE PLATFORM DESIGN07/30/2003
STRUCTURAL ANALYSIS:STRUCTURAL ANALYSIS:
–Integrated decks and hulls of floating platforms Integrated decks and hulls of floating platforms
involving large bulkheads are described by plate involving large bulkheads are described by plate
elements.elements.
–Deck shall be able to resist crane’s maximum Deck shall be able to resist crane’s maximum
overturning moments coupled with corresponding overturning moments coupled with corresponding
maximum thrust loads for at least 8 positions of the maximum thrust loads for at least 8 positions of the
crane boom around a full 360° path.crane boom around a full 360° path.
–The structural analysis will be a static linear analysis The structural analysis will be a static linear analysis
of the structure above the seabed combined with a of the structure above the seabed combined with a
static non-linear analysis of the soil with the piles. static non-linear analysis of the soil with the piles.
–Transportation and installation of the structure may Transportation and installation of the structure may
require additional analysesrequire additional analyses
–Detailed fatigue analysis should be performed to Detailed fatigue analysis should be performed to
assess cumulative fatigue damageassess cumulative fatigue damage
–The offshore platform designs normally use pipe or The offshore platform designs normally use pipe or
wide flange beams for all primary structural wide flange beams for all primary structural
members.members.
STRUCTURAL ANALYSIS:STRUCTURAL ANALYSIS:
–Integrated decks and hulls of floating platforms Integrated decks and hulls of floating platforms
involving large bulkheads are described by plate involving large bulkheads are described by plate
elements.elements.
–Deck shall be able to resist crane’s maximum Deck shall be able to resist crane’s maximum
overturning moments coupled with corresponding overturning moments coupled with corresponding
maximum thrust loads for at least 8 positions of the maximum thrust loads for at least 8 positions of the
crane boom around a full 360° path.crane boom around a full 360° path.
–The structural analysis will be a static linear analysis The structural analysis will be a static linear analysis
of the structure above the seabed combined with a of the structure above the seabed combined with a
static non-linear analysis of the soil with the piles. static non-linear analysis of the soil with the piles.
–Transportation and installation of the structure may Transportation and installation of the structure may
require additional analysesrequire additional analyses
–Detailed fatigue analysis should be performed to Detailed fatigue analysis should be performed to
assess cumulative fatigue damageassess cumulative fatigue damage
–The offshore platform designs normally use pipe or The offshore platform designs normally use pipe or
wide flange beams for all primary structural wide flange beams for all primary structural
members.members.
OFFSHORE PLATFORM DESIGN07/30/2003
Acceptance CriteriaAcceptance Criteria::
The verification of an element consists of comparing The verification of an element consists of comparing
its characteristic resistance(s) to a design force or its characteristic resistance(s) to a design force or
stress. It includes:stress. It includes:
a strength check, where the characteristic resistance is a strength check, where the characteristic resistance is
related to the yield strength of the element, related to the yield strength of the element,
a stability check for elements in compression related a stability check for elements in compression related
to the buckling limit of the element.to the buckling limit of the element.
An element is checked at typical sections (at least both An element is checked at typical sections (at least both
ends and mid span) against resistance and buckling. ends and mid span) against resistance and buckling.
Tubular joints are checked against punching.These Tubular joints are checked against punching.These
checks may indicate the need for local reinforcement checks may indicate the need for local reinforcement
of the chord using larger thickness or internal ring-of the chord using larger thickness or internal ring-
stiffeners.stiffeners.
Elements should also be verified against fatigue, Elements should also be verified against fatigue,
corrosion, temperature or durability wherever relevant.corrosion, temperature or durability wherever relevant.
Acceptance CriteriaAcceptance Criteria::
The verification of an element consists of comparing The verification of an element consists of comparing
its characteristic resistance(s) to a design force or its characteristic resistance(s) to a design force or
stress. It includes:stress. It includes:
a strength check, where the characteristic resistance is a strength check, where the characteristic resistance is
related to the yield strength of the element, related to the yield strength of the element,
a stability check for elements in compression related a stability check for elements in compression related
to the buckling limit of the element.to the buckling limit of the element.
An element is checked at typical sections (at least both An element is checked at typical sections (at least both
ends and mid span) against resistance and buckling. ends and mid span) against resistance and buckling.
Tubular joints are checked against punching.These Tubular joints are checked against punching.These
checks may indicate the need for local reinforcement checks may indicate the need for local reinforcement
of the chord using larger thickness or internal ring-of the chord using larger thickness or internal ring-
stiffeners.stiffeners.
Elements should also be verified against fatigue, Elements should also be verified against fatigue,
corrosion, temperature or durability wherever relevant.corrosion, temperature or durability wherever relevant.
07/30/2003 OFFSHORE
PLATFORM DESIGN
STRUCTURAL DESIGNSTRUCTURAL DESIGN
Design Conditions:Design Conditions:
OperationOperation
Survival Survival
Transit. Transit.
The design criteria for strength should relate to both intact and The design criteria for strength should relate to both intact and
damaged conditions. damaged conditions.
Damaged conditions to be considered may be like 1 bracing or Damaged conditions to be considered may be like 1 bracing or
connection made ineffective, primary girder in deck made connection made ineffective, primary girder in deck made
ineffective, heeled condition due to loss of buoyancy etc.ineffective, heeled condition due to loss of buoyancy etc.
PLATFORM DESIGN
STRUCTURAL DESIGNSTRUCTURAL DESIGN
Design Conditions:Design Conditions:
OperationOperation
Survival Survival
Transit. Transit.
The design criteria for strength should relate to both intact and The design criteria for strength should relate to both intact and
damaged conditions. damaged conditions.
Damaged conditions to be considered may be like 1 bracing or Damaged conditions to be considered may be like 1 bracing or
connection made ineffective, primary girder in deck made connection made ineffective, primary girder in deck made
ineffective, heeled condition due to loss of buoyancy etc.ineffective, heeled condition due to loss of buoyancy etc.
07/30/2003 OFFSHORE
PLATFORM DESIGN
CODES CODES
Offshore Standards (OS):Offshore Standards (OS):
Provides technical requirements and acceptance Provides technical requirements and acceptance
criteria for general application by the offshore criteria for general application by the offshore
industry eg.DNV-OS-C101industry eg.DNV-OS-C101
Recommended Practices(RP):Recommended Practices(RP):
Provides proven technology and sound engineering Provides proven technology and sound engineering
practice as well as guidance for the higher level practice as well as guidance for the higher level
publications eg. API-RP-WSDpublications eg. API-RP-WSD
BS 6235: Code of practice for fixed BS 6235: Code of practice for fixed
offshore structures.offshore structures.
–British Standards Institution 1982.
–Mainly for the British offshore sector.
PLATFORM DESIGN
CODES CODES
Offshore Standards (OS):Offshore Standards (OS):
Provides technical requirements and acceptance Provides technical requirements and acceptance
criteria for general application by the offshore criteria for general application by the offshore
industry eg.DNV-OS-C101industry eg.DNV-OS-C101
Recommended Practices(RP):Recommended Practices(RP):
Provides proven technology and sound engineering Provides proven technology and sound engineering
practice as well as guidance for the higher level practice as well as guidance for the higher level
publications eg. API-RP-WSDpublications eg. API-RP-WSD
BS 6235: Code of practice for fixed BS 6235: Code of practice for fixed
offshore structures.offshore structures.
–British Standards Institution 1982.
–Mainly for the British offshore sector.
07/30/2003 OFFSHORE
PLATFORM DESIGN
REFERENCESREFERENCES
W.J. Graff: Introduction to offshore W.J. Graff: Introduction to offshore
structures. structures.
–Gulf Publishing Company, Houston 1981.Gulf Publishing Company, Houston 1981.
–Good general introduction to offshore Good general introduction to offshore
structures.structures.
B.C. Gerwick: Construction of offshore B.C. Gerwick: Construction of offshore
structures. structures.
–John Wiley & Sons, New York 1986.John Wiley & Sons, New York 1986.
–Up to date presentation of offshore design and Up to date presentation of offshore design and
construction.construction.
Patel M H: Dynamics of offshore Patel M H: Dynamics of offshore
structuresstructures
–Butterworth & Co., London.Butterworth & Co., London.
PLATFORM DESIGN
REFERENCESREFERENCES
W.J. Graff: Introduction to offshore W.J. Graff: Introduction to offshore
structures. structures.
–Gulf Publishing Company, Houston 1981.Gulf Publishing Company, Houston 1981.
–Good general introduction to offshore Good general introduction to offshore
structures.structures.
B.C. Gerwick: Construction of offshore B.C. Gerwick: Construction of offshore
structures. structures.
–John Wiley & Sons, New York 1986.John Wiley & Sons, New York 1986.
–Up to date presentation of offshore design and Up to date presentation of offshore design and
construction.construction.
Patel M H: Dynamics of offshore Patel M H: Dynamics of offshore
structuresstructures
–Butterworth & Co., London.Butterworth & Co., London.
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