introduction to offshore structures-part-3

7/28/2019 Introduction to Offshore Structures-PART-3

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Types of loads

Categories of loads

Permanent (dead) loads

Operating (live) loads

Fabrication and installation loads

Environmental loads

Accidental loads

API-RP2A or BS6235


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Types of loads

PERMANENT (DEAD) LOADSWeight of the structure in air, including the

weight of grout and ballast, if necessary.

Weights of equipment, attachments or

associated structures which are permanently

mounted on the platform.

Hydrostatic forces on the various members

below the waterline. These forces include

buoyancy and hydrostatic pressures.


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Types of loads

OPERATING (LIVE) LOADSOperating loads arise from the operations on the

platform and include the weight of all non-permanent

equipment or material, as well as forces generated

during operation of equipment. More specifically,

operating loads include the following:

The weight of all non-permanent equipment

(e.g. drilling, production), facilities (e.g. living

quarters, furniture, life support systems,

heliport, etc), consumable supplies, liquids, etc.

Forces generated during operations, e.g.

drilling, vessel mooring, helicopter landing,

crane operations, etc.


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Types of loads

FABRICATION AND INSTALLATION LOADS

These loads are temporary and arise during

fabrication and installation of the platform or its

components.

During fabrication, erection lifts of various

structural components generate lifting forces,

while in the installation phase forces are

generated during platform loadout, transportation

to the site, launching and upending, as well as

during lifts related to installation.


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Types of loads

FABRICATION AND INSTALLATION LOADS


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Types of loads

ENVIRONMENTAL LOADS

Environmental loads are those caused by

environmental phenomena such as wind, waves,

current, tides, earthquakes, temperature, ice, sea

bed movement, and marine growth. Their

characteristic parameters, defining design load

values, are determined in special studies on thebasis of available data.


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Types of loads

ACCIDENTAL LOADS

Accidental loads are loads, ill-defined with respect to

intensity and frequency, which may occur as a result of

accident or exceptional circumstances.

Examples of accidental loads are loads due to collision

with vessels, fire or explosion, dropped objects, and

unintended flooding of bouyancy tanks.

Special measures are normally taken to reduce the riskfrom accidental loads. For example, protection of

wellheads or other critical equipment from a dropped

object can be provided by specially designed, impact

resistant covers.


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Types of weld joints


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Failure Modes

Elastic collapse Plastic collapse Fracture Surface damage

Excessive

Stretch

Twist

Bending

Buckling

Vibration

Excessive

Plastic

deformation

at room temp.

Creep at high

temperature

Cleavage or

Brittle Fracture

Fatigue Fracture

Stress rupture

Stress Corrosion

Cracking (SCC)

Hydrogen damage

Impact Fracture

Neutron induced

Fracture

General

corrosion

Pitting

corrosion

Fretting

Wear

Surface

coating &

Treatment

YieldStrength /

Creep

strength

Stiffness

Ultimate strength

Fracture Toughness


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Stiffness Design - Bending

Bending Stiffness = E * I


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Stiffness Design - Torsion

Torsional Stiffness = G * Ip


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Types of Fracture


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Types of Fracture


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Types of Fracture


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Types of Fracture


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Types of Fracture


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Types of Fracture


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Types of Fracture


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Types of Fracture


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Types of Fracture

introduction to offshore structures-part-3

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