Nautilus register marine consortium.

1. WELCOME
PRESENTATION ON
OFFSHORE PLATFORM DESIGN
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2. PLATFORM
INSTALLATION
• BARGE LOADOUT:
– Various methods are deployed based
on availability of resources and size of
structure.
• Barge Crane
• Flat over - Top side is installed on
jackets. Ballasting of barge
• Smaller jackets can be installed by
lifting them off barge using a
floating vessel with cranes.
– Large 400’ x 100’ deck barges capable
of carrying up to 12,000 tons are
available
www.nautilusregister.org/nrmc CSD PRESENTATION

3. CORROSION 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.
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4. PLATFORM
FOUNDATION
• FOUNDATION:
– The loads generated by environmental
conditions plus by onboard equipment
must be resisted by the piles at the
seabed and below.
– The soil investigation is vital to the
design of any offshore structure.
Geotech report is developed by doing
soil borings at the desired location,
and performing in-situ and laboratory
tests.
– Pile penetrations depends on platform
size and loads, and soil characteristics,
but normally range from 30 meters to
about 100 meters.
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5. NAVAL ARCHITECTURE
• HYDROSTATICS AND STABILITY:
– Stability is resistance to capsizing
– Center of Buoyancy is located at center of
mass of the displaced water.
– Under no external forces, the center of
gravity and center of buoyancy are in
same vertical plane.
– Upward force of water equals to the
weight of floating vessel and this weight
is equal to weight of displaced water
– Under wind load vessel heels, and thus
CoB moves to provide righting
(stabilizing) moment.
– Vertical line through new center of
buoyancy will intersect CoG at point M
called as Metacenter
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6. NAVAL ARCHITECTURE • HYDROSTATICS AND
STABILITY:
– Intact stability requires righting
moment adequate to withstand
wind moments.
– Damage stability requires vessel
withstands flooding of
designated volume with wind
moments.
– CoG of partially filled vessel
changes, due to heeling. This
results in reduction in stability.
This phenomena is called Free
surface correction (FSC).
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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
CSD PRESENTATION

7. STRUCTURAL DESIGN
• Loads:
• Offshore structure shall be designed for
following types of loads:
– Permanent (dead) loads.
– Operating (live) loads.
– Environmental loads
» Wind load
» Wave load
» Earthquake load
– Construction - installation loads.
– Accidental loads.
• The design of offshore structures is
dominated by environmental loads,
especially wave load
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8. STRUCTURAL DESIGN
• Permanent Loads:
Weight of the structure in air,
including the weight of ballast.
– Weights of equipment, and
associated structures permanently
mounted on the platform.
– Hydrostatic forces on the members
below the waterline. These forces
include buoyancy and hydrostatic
pressures.
www.nautilusregister.org/nrmc CSD PRESENTATION

9. STRUCTURAL DESIGN
• Operating (Live) Loads:
– Operating loads include the weight of all non-
permanent equipment or material, as well as forces
generated during operation of equipment.
• The weight of drilling, production facilities,
living quarters, furniture, life support systems,
heliport, consumable supplies, liquids, etc.
• Forces generated during operations, e.g. drilling,
vessel mooring, helicopter landing, crane
operations.
• Following Live load values are recommended in
BS6235:
Crew quarters and passage ways: 3.2 KN/m2
Working areas: 8,5 KN/m2
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10. STRUCTURAL DESIGN
• Wind Loads:
• Wind load act on portion of platform above the
water level as well as on any equipment,
housing, derrick, etc.
• For combination with wave loads, codes
recommend the most unfavorable of the
following two loadings:
– 1 minute sustained wind speeds combined
with extreme waves.
– 3 second gusts.
• When, the ratio of height to the least
horizontal dimension of structure is greater
than 5, then API-RP2A requires the dynamic
effects of the wind to be taken into account
and the flow induced cyclic wind loads due to
vortex shedding must be investigated.
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11. Thank You
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