LO1 Structures Flashcards
What are the three methods when carrying gas cargos?
-Pressurisation under normal temperature.
-Refrigeration and pressurisation.
-Refrigeration under atmospheric temperature.
What are the advantages of Pressurised Carriers?
- The ship hull is built using ordinary grades of steel as the cargo is carried at
ambient temperature and no insulation is required.
-No reliquefication plant is required. - Operations are simpler.
What are the disadvantages of gas Carriers?
- Due to the spherical tank shape, the use of underdeck space is not well
optimised. - High design pressure requires considerable tank wall thickness, with
consequent increase in displacement weight and cost. - The weight in tonnes of cargo carried is lower than for a refrigerated ship of
similar size, due to cargo density difference.
What are the advantages to semi-refrigerated carriers?
- More cargo can be carried in a tank of the same capacity.
- A tank of the same capacity is lighter and cheaper to build.
- Much larger and more economical ships can be constructed.
what is a fully-refrigerated gas carrier?
These ships carry cargoes at approximately atmospheric pressure and are designed
to transport large quantities of LPG and ammonia between terminals equipped with
fully refrigerated storage tanks.
What are the hazards of gas carriers compared to petroleum carriers?
-Extreme cold from leaks and spillages which can effect the ductility of the ships structure.
- Potential contact by personnel via liquid or gas leaks causing severe frost burns.
-Rupture of the pressure system (LPG) causing massive evolution of vapour and subsequent explosion hazard on a significant scale.
What type of alloy is used in the construction of the tanks ?
-Carbon steel.
-Steel with temperature limits down to -55 (found in IGC code).
Why is insolation materials fitted to the tanks?
-To minimise heat flow into cargo tanks, reducing the likelihood of ‘boiling-off’.
-To protect the ship structure around the tanks from the effects of low temperature.
What characteristics must the material have to be used as insulation?
- Low thermal conductivity.
- Ability to withstand mechanical damage.
- Light weight.
-Unaffected by cargo liquid or vapour.
What are 3 types of materials used for insulation and where are there applications?
-Balsa wood (Load-bearing insulant).
-Mineral wood (Supplied in slabs or rolls).
-Polystyrene (pre-formed, sprayed or foamed).
What indicator functions are found in the central control system?
-Fixed fire detection/fire alarm system.
-Automatic sprinkler and alarm system.
-Fire door/watertight door indicator panel.
-fire door closure panel.
What is a ‘class C’ division?
-Constructed of non-combustible materials and they don’t need to comply with requirements relevant to the passage of smoke or flame nor limitations to temperature rise.
What is a combustible material?
Materials that can easily ignite or burn.
What is a control station?
Where the ships radio and main navigation equipment or the emergency source of power is located or where fire recording or fire control equipment is centralised.
What is a materials flashpoint?
The temperature at which a product will give off enough flammable vapour to be ignited as determined by the approved flashpoint apparatus.
