Offshore Engineering Structures and loading

Question 1

Design specifications

Materials

Working life ( >25 years)

Loading of platform - provide safe working environment for people onboard

Environmental- corrosion and weather/ sea state

Maintenance - underwater

Answer 1

Changes to uk regulations

1988. Piper alpha

Health and safety executive (HSE)
Offshore installations regulations 1992

Created duty holder ( owner of the platform)

Created “Saftey cases” demonstrates the ablility to control major accident risks effectively.

This was revised in 2005

Duty holder to conduct a review of the safety case every 5 years

Question 2

Design considerations

Sustain loads during all operating and damaged conditions

• maintain safety for all personnel
• adequate durability against deterioration
• comply with relevant practises
• inspection maintenance and repair work

Answer 2

Design considerations

Limit states

• ULS ( ultimate) relating to the ultimate resistance for carrying loads
• FLS ( fatigue) possible failure due to effect of cyclic loading
  ALS. (Accidental) damage due to accidents
  SLS. ( serviceability) normal use and durability

Question 3

Types of offshore structures

• concrete structures
• jack ups
• semi submersible
  -drill ships
• compliant towers
  -5”tension leg floating platform
  -floating production systems
• single anchor leg moorings
• ## single buoy mooring

Answer 3

Know all structures.

Question 4

Loading of structures.

What is stress

Answer 4

Stress is load(force) over area

Question 5

Loading structures.

Types of stress.

Tensile - atoms are pulled apart. ( moving or lifting)

-compressive - atoms are pressed together ( squeezed)

Answer 5

Normally

Tensile stress is thought to be positive stress and compressive as negative stresses

Question 6

Loading

• Bending - material is under stress from loading on the top

Answer 6

bending - on the top where load is applied you get compression stress as the material bends and tension stress underneath.

Question 7

Shear stress

Atoms are pushed passed one another

Answer 7

This is also referred as torsion

Question 8

Properties of materials

Properties to consider are
- yield strength

Answer 8

The stress at which material begins to deform plasticslly

Question 9

Elongation

Answer 9

Measure of ductility

Question 10

Toughness

Answer 10

Resistance to fracture.

Question 11

Electrical and thermal conductivity

Answer 11

Materials conductivity to electric and temperature

Question 12

Density

Answer 12

Weight per volume of material

Question 13

Hardness

Answer 13

Wear resistance

Question 14

Yield stress

What is yield stress

What is yield load

What is yield point

Answer 14

Yield stress is when material is loaded and components bend and move ellasticly when the load is removed it returns back to its shape

Yield point is the point in which if the force is continued past the material will deform and not reutrn back to its normal shape. Like if it’s been dented or bent. This has been loaded past its yield stress

Question 15

UTS

Ultimate tensile strength.

Answer 15

If loading is continued well into the yield region it reaches a known max value known as the UTS

Question 16

Types of fracture

Ductile. Brittle

Answer 16

Ductile
- this type of fracture is characterised by significant plastic deformation prior to and during cracking extension.

Brittle -
Rapid propagation of a crack and can occur eat appliedstress significantly below the yield strength levels with no prior warning.

Question 17

Fatigue fracture

Answer 17

Failure of experienced materials under cycli stress

Discontinuities such as welds and changes in section material flaws are favoured sites for fatigue failure

Question 18

Forced to a structure

Answer 18

Steady

Cyclic

Question 19

Drag force to a structure.

Answer 19

The steady force of a fluid as it passes a stationary structure is known as the drag force.

Question 20

Drag force calculations

Answer 20

Double the flow speed and the drag force is increased by 4 times. (Square root formula)

Changing the shape of the object may reduce the force