Short Note On Oil Tankers Cargo System

Definition: Sublimation: solid directly changes into gaseous. Boiling pint: temperature that liquid boiling when heat is supplied to it at atmospheric pressure. Viscosity: the property of fluid by virtue of which they offer a resistance to flow. Flash point: the lowest liquid temperature at which the small flame initiates a flash or flame across the surface or liquid. Manifold valves: cargo is loaded or discharged via shore hoses or metal loading arms which connect to the athwartships deck pipeline known as manifolds. Drop valves: each of the main tank pipelines has a counterpart on deck and loading line which lead vertically from deck lines to the tank lines are known as drop lines. Each main line has one or two drop lines and drop valves control the flow of the oil in those lines. Master valves: at each place where a fore & aft pipeline passes through a bulkhead a valve is fitted in the line. This is kwon as a master valve and separates tank served by the same fore & aft line. Crossover valves: athwartships tank lines joining the main lines are known as crossover lines and crossover valves separate the main line from each other as well as separating individual tanks in other word crossover valves separated in athwartships direction. Tank valves: close to each bellmouth is located a valve which controls the flow of the oil into and to of the tank. Cargo pumps: there are two basic types of cargo pumps on oil tankers positive displacement & centrifugal both of which are usually driven by steam. Displacement pumps: This type of pump moves a certain amount of liquid with each pump cycle. The pump piston draws liquid though a non-return suction valve into a cylinder which is known as a bucket. The cylinder is full at the end of the suction stroke and on the reverse stroke the liquid is expelled from the cylinder through a non-return discharge valve. Most pumps of this type are duplex having two buckets and two pistons which ensure that suction is not lost at the end of a stroke. Positive displacement pumps move a low volume of oil at relatively high pressure. Their use on tankers is generally restricted to stripping pumps. Centrifugal pumps: An impeller, which is inside a casing, physically moves the oil by means of a throwing movement which is similar to the expelling of water from the bicycle tire when cycling in wet weather. The oil is sucked into the casing via a discharge valve. The pump provides a continuous flow of oil and it is powered by a steam turbine drive unit which, for safety reason, is installed in the engine room. Centrifugal pumps move large volumes of liquid at a relatively low pressure and consequently are generally used as main cargo pumps (mcps). Main source of ignition on tankers: 1. Smoking 2. The galley 3. Electrical equipment 3. Sparks 5. Lighting 6. Metal 7. Domestic equipment 8. Aluminum 9. Tank anodes 10. Ship to shore electric 11. Static electricity 12. Spontaneous combustion Precaution to prevent ignition due to static charging: • During tank washing never introduce metal objects into the tank. • At least 30 minutes after completion of loading should be used from hand held or other conductive equipment. Ship/shore safety check list: This is join list provided by the terminal and which is signed by a ship and a terminal representative; 1. Appropriate personal notified that the cargo operation are about to commence. 2. Sufficient personal available for cargo watch to manifold. 3. Warning notified displaces no smoking & no naked light. 4. Fire application ready for immediate used. 5. Mooring tight and emergency towing wire correct positioned. 6. Agree ship/shore communication system working. 7. No unauthorized work to the carried out.

8. No unauthorized persons on board. 9. Safe lighting available. 10. Galley precaution observed. 11. Cargo tank lead closed. 12. Manifold drip trays in use. 13. Tank inert and inert gas system checked. 14. All doors and ports to accommodation closed. 15. Air conditioning unit on internal air recycling. 16. Safe ship/shore access. 17. Tank ventilation system checked. 18. Ship ready to move under own power. 19. Emergency shutdown understood. 20. Appropriate flag and light signal to be show> 21. All deck scuppers plugged to prevent oil leaks over board. 22. No unauthorized craft alongside. 23. Cargo line properly set. All v/vs not in use closed and lashed. 24. All necessary spark arresters in good condition in place. Describe the safety and operational precautions for loading a full cargo of crude oil into vlcc: 1. Tend mooring. 2. Tend the gangway and watchman, must be on duties. 3. Calculate the rate of loading. 4. Check fire wires are correctly rigged and ready to use. 5. All watch men on duty must be check regularly for oil pollution. 6. Ensure not hot work on board. 7. See and act ship to shore check list. 8. See all tank lids are closed and safe ventilation is being carried out. 9. Ensure which oil loading into correct tank. 10. Maintain state of list and trim as required. 11. Enforce no smoking, regulations. 12. Ensure red light B flag is displayed. 13. Permit, use of safe torches, only. 14. No unauthorized persons on board. 15. Make sure all company and port regulations are observed. 16. Ship ready to move under own power. 17. Check that inert gas system is ok. 18. Manifold drip tray is positioned. 19. All access to accommodation is closed. 20. Ensure all deck scuppers plugged to prevent oil leaks overboard. 21. See that the loading plan is observed and followed. 22. All fire fighting equipment ready for immediate use. Precaution for valve: 1. Use wheel key for opening & closing the valves. 2. Use a rope for indicating the opening or closing of the valves position. 3. Cargo valves have to be tested from time to time. To ensure the valve is in good condition & no have leakage. 4. At all time of working on cargo the sea valves must be closed. 5. The testing must be set by standing orders of chief officer. 6. The opening of valves must be done slowly by one turn.

Ring main system Advantage: In this system any tank can be discharged by any pump. Thus different grade of the cargo can be loaded. Disadvantage: • It is expensive to build due to the extra length of the piping required. • Extra bend is required. Thus decreasing in rate.

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Risk of leakage from radius of bend exists.

Ring main sys

Free flow system Advantage: • Main pipe line is not used for discharge. • Less pipe line. • Less bend. • Less friction & more pressure cause very high discharge. Disadvantage: • Is not flexible. • One grade is dischargeable if more risk of contamination exists. • Risk of overflow exists if level of all tank doses not carefully monitoring.

Free flow system

Direct line system Advantage: 1. Quick loading & discharging. 2. Short pipe line. 3. Less bend. 4. Less loss of pressure due to pipe line friction. 4. 5. Direct line to provide better suction. 6. Time of washing the line is short.7. System is cheaper than the other system.8. Leak is minimized. 9. Easy to operate so less training is required.10. It is easy to separate each cargo. Disadvantage: a. Incase of leaking the control of leakage is difficult. b. This system is very inflexible.

Direct line system