Offshore Platform 
                     WELCOME
PRESENTATION ON 
OFFSHORE PLATFORM DESIGN
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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
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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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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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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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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).
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
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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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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.
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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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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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Thank You
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