Cargo Operations for Tanker I 58.
Ship Draft
“A mate should be very careful while a surveyor uses his sampler. Often surveyors take cargo samples at the discharge port and send them for analysis
before commencing discharge to verify that no discrepancies are observed between load port samples and discharge port samples. For sampling, they use ship‟s sampler or their own samplers. Often their samplers are found with loose ends, and as a result, sample bottles fall inside the tank. These bottles during trim can reach the aft section of the tank and near the suction well of the pump.
Sometimes these bottles get trapped inside a deep well pump‟s casing, thereby seizing the pump”.
independent line system using individual deep well pumps mounted inside all tanks. Following steps to be taken for discharge operation:
• The inert gas plant should be fully operational and functional before starting any cargo pump
• All branch IG valves for tanks must be opened
• The deck main isolating valve should be fully open
• Before discharge using steam-driven COPs, always ensure that the separators of the pump to be used are filled with liquid cargo. If not, they can be filled by opening the bottom cargo lines of the tanks going to the pumps
• Initially, the line up should be made to recirculate
the cargo in a loop, i.e. to take suction from 4Ws and pass the cargo through the pump, which makes it pass through the deck line master valve and
drops back into the cargo tank 4Ws via the drop valves. This should be done at minimum RPM
59. l Marine Insight Cargo Operations for Tanker I 60.
• The Chief Officer will check the deck preparation for discharging of the cargo. Once all checklists are completed and the setup is satisfactory as per the cargo discharge plan, he/she will contact the shore facility representative to inform the ship
preparedness
• Once the shore terminal confirms that the facility is ready to receive cargo, the chief officer will instruct the deck watch to open the designated valve as per the cargo plan. The manifold valve can be opened slowly, and the drop valves of the same line can be closed
• Once the drop lines are closed, the cargo starts passing to the manifold and over to the terminal.
This should be confirmed by a deck watch who would then verify cargo passing through the line and the pressure at the manifold
• The initial discharge to commence at reduced speed, and once the shore representative confirms that there are no oil leaks and the cargo is going into the designated tank, the pumping rate can be increased to the pressure as decided in the ship- shore meeting
61. l Marine Insight Yard Delivery Procedure l 62.
Reviewing Checklists and Paper work
• As the cargo passes through the manifold, the deck watch person should confirm the manifold
surroundings and the pump room area should be cleared of any unwanted oil discharge or leaks
• The engine room can then be notified to increase the steam pressure for increasing the RPM of COPs or to start more pumps to comply with the required discharge rate
63. l Marine Insight
• As more pumps are required more tanks can be opened, or pumps can be made common using the pump crossovers in the pump room. At the same time, open bottom crossovers in tanks to ensure that the fluid keeps flowing to the pump
“If pumps are running idle for sometime before commencing discharge or inbetween, re-circulating cargo within the line is a better method of keeping the pumps idle than closing the discharge valve. Keeping the discharge valve closed with the pump running can lead to the churning of cargo, which raises casing and bearing temperature above allowable limits.”
Cargo Operations for Tanker I 64.
COP Arrangement on Ship
• Once both the pumps have started, they must be run at same discharge pressure and their pressure must be increased slowly and deliberately to avoid pressure surges. The cargo tank ullages must be monitored frequently during the initial stages to ensure that the cargo is getting discharged only from the required tank and not getting transferred to other tanks
65. l Marine Insight
• All the joints and flanges on the deck and in the pump room must be checked visually to ensure no leaks are present when pumps are running at
maximum load. Simultaneously, ballast pumps must be started to contain shearing forces and bending moments within the permissible limits
• If all tanks are 95% full or above, always de- bottom all the tanks up to 90% or less and then commence bulk discharge or group-wise
segregation to avoid cargo overflowing on deck in cases where trim or list exceeds extreme values
“As the initial stage starts to settle down with pumps running normally, the pressure is kept to a minimum, and the cargo is discharged through required tanks only. The connections are thus proved and the pumps can be increased to the maximum required RPM to attain bulk discharge rate.”
Cargo Operations for Tanker I 66.
Checking Ullage During Cargo Operation
• A portable Framo pump is provided onboard in case any of the pumps malfunctions. The hydraulic lines on deck are equipped with manifolds to
connect to the portable pump
Deck Watch and Personnel Arrangement
• Once the shore-ship side is ready for cargo
unloading, open the manifold valves, and start the first cargo pump at slow speed
67. l Marine Insight
• Deck watch to confirm that there are no oil leaks from piping joints and no oil is flowing out of the tanks other than the tank being used
• Once the operation is running smoothly, open delivery valves to start pumping oil and other pumps as per the plan
• Follow the terminal representative instruction to increase the manifold pressure to the agreed pressure
• The deck watch shall continuously check for oil leaks in the cargo area throughout the oil discharge operation
• When discharging multiple grades, care needs to be taken to isolate the correct valve and to stop the pump as required
“A good discharge plan will always maintain group wise segregation between tanks so that when cargo levels are low, individual pumps can be run in
respective groups and staggered in such a way that as the stripping of one group is done the next 2 groups are running at their maximum rate”.
Cargo Operations for Tanker I 68.
• The level gauges of all discharging tanks to be continuously monitored. More care to be taken when the shore tanks are of a greater height, which can cause back pressure and filling back of ship's cargo tanks
• To stop the cargo pump, reduce the pump RPM to the minimum, fully close the delivery valve, notify the engine department, and then stop the pump
• Ballasting and de-ballasting to be carried out as per the ballast plan, after taking permission from the harbor master
• Precautions need to be taken for deciding heated cargo discharge i.e. not filling the adjacent ballast tank if the cargo is heated in the hold
69. l Marine Insight
• Ensure ballast tank is not filled over 90% of the tank level
Cargo Operations for Tanker I 70.
Shore Storage Tank
Trim and Draft
Trim and draft plays an important role during the discharge operation as the suction mouth of the pump is usually located at the aft end of the tank and the trim aft will help strip the cargo from the tank. Trim and draft are regularly checked during the operation and the trim is applied as described in the COW manual for stripping the cargo tank.
Ensure the draft maintained after allowing for tidal
71. l Marine Insight
variation is well within the height limitation of manifold / loading arms.
Efficient Operation of Centrifugal Cargo Pumps
The standard practice to operate the centrifugal pumps is to run at full nominal RPM, especially during bulk discharge.
Both the pumping efficiency and pumping rate are affected when the pump is run at reduced RPM.
Once the tank level goes down and the ullage touches low-level values, it is always advisable to partially close the discharge valve instead of reducing the pump revolutions. This is done to reduce the flow rate and also to prevent cavitation in the pump (pump sucking gas at suction side due to vortex formation/
gasification).
Cargo Operations for Tanker I 72.
Ship Trim Aft
If the pump is operated incorrectly and inefficiently (e.g. pump is trying to discharge more cargo than
entering the suction side), the chances of cavitation will increase.
This usually happens with high viscosity cargo or where the cargo is highly volatile (high RVP cargoes).
The tank IG pressure plays a critical role in increasing the pump's Net Positive Suction Head.
If the cargo pump is drawing gas or air in the suction instead of fluid, the pump would then be operating in a partial vacuum instead of the fluid. The suction pressure is a critical parameter to know about the
73. l Marine Insight
cavitation in the cargo pump. Vibration in the pump will increase the cavitation rate.
A responsible officer on watch in the cargo control room (CCR) must observe the tachometer and the discharge pressure, and be prepared to operate
("throttle") the pump discharge valve once the pressure falls or to shut down the pump if it loses suction.
"A 40% open butterfly valve will allow nearly the same flow rate as a 100% open butterfly valve. The RPM can always be reduced as necessary".
Cargo Operations for Tanker I 74.
Monitoring Parameters in CCR- Image Credit: Sarthak Nayak
The Auto Unloading System (AUS) shall be correctly and effectively utilized to reduce the overall discharge time.
Procedure for Starting Portable Framo Pump
• Connect the hydraulic manifolds provided in the hydraulic deck lines (They run forward to aft for providing hydraulic oil to the cargo pumps). Keep the inlet and return valves supplied near the
hydraulic manifold closed
• Connect the flexible suction and discharge hoses to the portable Framo pump
• Rig the assembly over the tank hatch using a tripod, lower it slowly into the liquid and fix it firmly to the cargo pump. Vibration in the pump will increase the cavitation rate.
75. l Marine Insight
• Slowly open the inlet and return valves. Initially, keep the hydraulic system pressure low up to 60 bars
• As the pump starts running, check all hydraulic, suction and discharge hoses are capable of withstanding the operation
Cargo Operations for Tanker I 76.
Operating Portable FRAMO Pump
• If all is confirmed in order slowly increase the system pressure as required
77. l Marine Insight
Completion of Discharge
• Once the cargo operation is called complete from ship and shore side, the manifold gate valve is to be closed
• After the completion of a dry survey by the terminal, the hoses and arms connected to the manifolds are to be drained before disconnection
Cargo Operations for Tanker I 78.
Portabkle FRAMO Pump piping
Manifold Valves
“The Chief Officer should frequently check ship stability and hull stresses to ascertain that they are within permissible limits. These checks shall be constantly performed during ballasting/deballasting and upon cargo operation completion.
• Once the draining operation is finished, tank valves and vent valves are to be closed
• The duty officer must ensure that the connection is depressurized and isolated from the internal cargo tank IG pressure
79. l Marine Insight
• Deck watch must check the ullage and the quantity remaining in the tanks, from which, cargo has been unloaded
• After completion of the cargo operation, ullage ports, vapour locks and all other tank openings to be closed
• Care should be taken to ensure that cargo lines do not become over-pressurized due to high ambient temperatures
Cargo Operations for Tanker I 80.
Deck Watch Keeping a Check
• The Inert Gas System recorder to be switched on to record and monitor the cargo tanks pressure
• After adjusting the inert gas pressure in tanks, the IG system to be stopped when the pressure
reaches the prescribed value (usually 1000 mmAq) 81. l Marine Insight
Cargo Completion Survey
The cargo completion survey is done by the terminal surveyor, who after satisfactory inspection, issues the "
Dry certificate / ROB certificate.
Cargo Operations for Tanker I 82.
Inert Gas Generator Panel
Surveyor Making Records
The deck watch officer must attend the terminal surveyor or berth master when cargo tank gauging is done to confirm the tank is free from pumpable (liquid) cargo. Any remaining Un-pumpable cargo must be documented with suitable remarks on the certificate.
The vessel is to prepare a dry certificate or ROB certificate (in case the cargo tank contains pumpable liquid). The deck officer or chief officer should insist for the copy of the surveyor's document for onboard documentation.
Recordkeeping in Tanker Cargo Log Book
Following items shall be recorded in Tanker Cargo Log Book on hourly basis :
• Discharged Quantity (Rate) to compare it with that
83. l Marine Insight
of the terminal side
• Cargo levels (ullage) in tanks not being used
• The pumping performance record/pumping log
• PumppPressure and RPM
• Manifold pressure / temperature
• Draft & Trim
• Stress and Stability of the vessel
• Tank pressure
• Issue time and date of the dry certificate or ROB certificate
Cargo Operations for Tanker I 84.