Tanker Operation: Standard Equipment For Prevention Of Oil Spillage
There exists an inherent risk of oil spillage while handling oil cargo on board an oil tanker. However, good prevention initiatives can go a long way in reducing the risk of oil pollution from ships. In the event of any oil spillage from the ship, it is necessary to ensure that effective preparedness measures are in place to ensure a timely and coordinated response to limit the adverse consequences of pollution incidents involving oil and hazardous and noxious substances (HNS). We have summarized below some fundamental guideline for safe handling of oil cargo.
Cargo Tank Level Measuring System and Level Alarm System:
Portable tank gauging equipment is to be in a state of readiness and checked before arrival ports.
Automatic high-level alarms and independent overfill alarms shall be checked before the Cargo oil loading operation, using the appropriate ANNEXES of "Tanker Loading Checklist" and "Tanker Discharging Checklist."
Every Quarter, the Fixed Cargo Tank Level Gauge Alarm Setting and Portable Gauge Record should be verified using the "Quarterly Testing Record for Miscellaneous Equipment"
Emergency Hydraulic Hand Pumps shall be ready to use in the Pump room and at Manifold.
Also, a crew member on deck duty should be familiarized to operate the Hand Pump and "Emergency Push Switch" of Hydraulic Solenoid Valve in Hydraulic Valve Local Stands.
“Software”/Guidelines For Prevention Of Oil Spillage
Pay strict attention to Cargo Tank Level Gauges (Fixed & Portable)
To prevent marine pollution caused by oil overflow, strict attention must be paid to all tank level gauges and high-level alarms.
At Loading Ports, the accuracy of the fixed level gauges and the integrity of that cargo tank valve should be ascertained, well before reaching the Final Topping-off Ullage, using "Cargo Tank Level Gauge Check Record at Loading Ports."
A close watch is to be kept at the manifold back pressure build-up during such operations.
If there is a reason to suspect that the automatic level gauges are inaccurate during loading operations, the level shall be confirmed by the portable gauging tapes.
Topping off operations should be carried out using portable gauging tapes.
During any oil cargo transfer operation, level gauges in all cargo tanks, ballast tanks, including those tanks which are not being loaded or discharged, must be monitored.
The level in tanks must be recorded in the "Tanker Cargo Work Logbook" hourly throughout the transfer operation.
On completion of loading in the tank, the level should be locally monitored for a while (even after the closing of the respective valve). Afterward, a periodic check needs to follow.
During COW (crude oil washing), close attention must be paid to the level gauges in the Receiving (Gathering) tank in order to prevent oil cargo overflow.
Operation Guidelines for Cargo / Ballast valves
''Repeat the Order (Answer Back)''
A work order shall be repeated by the receiver for acknowledgement. On successful completion, he shall report the details for confirmation.
Confirmation on Valves Setting prior to Cargo Oil Transfer Operation
Chief officer shall do or instruct the duty officer to check & set pipe lines in Cargo control Mimic panel by pointing a finger to avoid mistakes.
For Manual valves, the open / closed condition shall be correctly indicated and updated, after positive confirmation from personnel at the site.
Before commencement of oil handling, a complete line setting shall be double checked by an independent person. In case of complicated valve operation, the ship specific “Valve Checklist” shall be used prudently.
Fig: Oil pollution at sea
The Chief Officer shall instruct crew to confirm, once again, the pipe lines to be used before commencement of the oil handling work, and indicate the valves to be opened or closed, and shall confirm being opened or closed.
The Chief Officer shall confirm in the same manner in case of change of oil types, suspension and restart of cargo handling, ballasting or de-ballasting.
Opening and Closing of important valves must be supervised and witnessed by an officer.
Opening and closing certain important valves, including Pump room Sea valves, Overboard discharge valves, and Manifolds valves shall be carried out under the chief officer's supervision or the deck duty officer designated by the chief officer.
Before commencement of cargo oil transfer operations, the Chief Officer or the deck duty officer shall confirm that the Pump room Sea valves are closed and shall ensure that the valves are sealed.
Warning Notices should be posted at such valves' locations leading to overboard where there is a possibility of oil / oily effluence discharge.
Such notices should caution personnel against opening without the Chief Officer's permission.
Blind flanges shall be inserted in all Overboard discharge valves and Sea valves.
Prevent Erroneous Operation of Valves
To ensure that valves are operated following the Cargo Oil Transfer Plan, any operation of cargo valves before, during, and upon the completion of cargo oil, transfer operation must occur under the supervision of the Chief Officer or the duty deck officer.
Before arrival to the terminal all Cargo, Ballast valves & remote indicators shall be checked for its status (Open / Close).
The "Valve Checklist" should be used prudently.
Valve Handling with Avoiding Liquid Hammer
Strict attention must be paid to the vessel's trim during discharge operations. If the vessel has excessive trim by the stern, it may be necessary to partially close / fully close the cargo valves to the aft of oil cargo tanks being discharged to prevent cargo from flowing from the forward tanks to the aft tanks. It is due to apparent differences in the liquid head. Such could cause cargo overflow and oil spill from the aft tanks.
Oversee pressure gauges in operating tank suction valves. To avoid damage to valves and pumps, careful attention must be paid when opening suction valves in cargo tanks. This crucial when the tank is full or almost full of cargo.
The status of the filling (full or empty) of the planned bottom line to be used should be controlled before connecting that tank to the pump.
The vacuum may exist on the valve's suction side, causing the cargo to flow towards the Pump at excessive rates. Always open the valve very carefully and slowly while watching the pressure gauge on that line.
Securing Indication for Closed Valves
All the vessel's cargo lines, bunker line, and tank cleaning line valves should be marked in such a manner as to be unmistakable to personnel as to what valves they are operating. Manually operated valves on these lines, including the pump room valves, should be marked/numbered.
Handwheels on manual valves shall be secured with a rope or twine to indicate its closed position. Valves that may be required to be opened in an emergency must be secured in a way that can be easily opened.
Suitable securing arrangements should also be carried out for ancillary valves to sea chest arrangements (testing/blowing vent pipes in the pump room, etc.) to prevent accidental opening.
Opening / Closing Speeds of Valves should be checked quarterly using "Quarterly Testing Record for Miscellaneous Equipment" and compared as per original timings, as specified by manufacturer.
Prevention of Internal Pressure increase by Expansion and by Blocking (Solidification)
Oil or liquid left inside a closed system of piping can create severe damage to the system or cause leakage/rupture of gaskets, expansion joints, or flanges due to expansion inside as the liquid temperature rises inside the system.
While having this incident on deck could cause oil pollution, it might trigger cargo contamination if it occurs inside tanks, e.g., Bottom Cargo pipelines, Pumproom pipelines, Top Loading lines & Small diameter lines, including COW lines, etc.
To avoid damage, the following must be observed:
The cargo oil transfer plan shall include instructions on how to displace oil cargo in the lines upon completion of transfer operations.
This must be discussed with shore facility representatives.
Cargo oil should never be left in the deck or pump room cargo piping upon completion of cargo oil transfer operations but should be dropped into the cargo tanks.
Close attention shall be paid to cargo bottom lines containing non heated cargo that passes through tanks loaded with heating cargo.
Sometimes, ballast water left inside pump room lines without proper monitoring/measures could leak at flanges. Such situations are more likely experienced when proceeding to warmer regions.
Similarly, after heated cargo is loaded or discharged, preventive measures against solidification inside pipelines should be taken.
Bottom lines containing such, particularly in the way of empty cargo tanks, need to be considered for stripping after completion of operations.
For additional details for heating cargo, refer to "Crude Oil Washing with Heated Cargo"
Air in such locking systems, can be more readily compressed and cause less damage, as compared with liquid entrapped in a closed system.
Guideline for Pump room Sea Chest Valve Operation
The "Cargo Sea Chest" shall NOT be opened without office permission except in case of emergency.
If the sea valves are required to be opened for taking ballast or washing water, the residual oil in line shall be completely stripped; Pump shall be started first.
After confirming sufficient vacuum in suction gauge, the concerned sea chest valve shall be opened in the presence of the Chief Officer.
Sometimes in port, it is required to carry out line displacement of shore hose at high discharge rates using the cargo oil pump- after completion of discharge operations.
Where there is limited time for awaiting the tank's filling using the connection provided using the fire line, the next choice to consider is using the ship's fixed pump room connection to take suction from a ballast tank with sufficient positive head.
Precautions, as mentioned above, to be exercised.
Inspection for the Sea-chest
Before entering the first loading port and first discharging port, the presence of oily ingredients shall be checked using the cocks and air cocks provided to sea-chests.
The integrity of the sea chest should be verified by pressure testing before entering ports, as described above. Care should be exercised not to exceed 3.5 Kg/cm2 pressure inside the system.
This shall be recorded in the Annexes of the 'Tanker Loading Checklist' and 'Tanker Discharging Checklist.'
Inert Gas System / Scrubber Cooling Pump operation
For discharge ports of environmentally sensitive nature, where the Air pollution and Scrubber discharge flushing could interfere with the ecosystem, the Inert Gas System shall be run before embarking the harbor pilot when entering the port.
This is done so that the IGS plant can settle down & avoid dark funnel smoke emissions on start-up.
The internal memory battery within the CP Unit is to be replaced as per manufacturers recommended interval and suitably indicated at the external portion.
Safe Mooring In Port
Always keep in mind that Mooring Failure on Oil Tankers shall be involved with accidental Cut of Manifold Cargo Line Connections, what means to occur "Major Oil Pollution"
During cargo oil transfer operations, the deck duty officer and the deck cargo watchstander must pay strict attention to moorings throughout the transfer operation to avoid damage to loading / discharging arms and flexible hoses.
As the vessels' draft changes during the transfer operation, mooring ropes and Brake's tension must be correctly adjusted and set to avoid the vessel's motion.
Suitable visible marking arrangements should be employed at the Manifold and closely monitored during the adjusting of mooring ropes.
The vessel is always maintained within the operational envelope of manifold arm connections.
When adjusting moorings, it is important to ensure that the load is distributed to all mooring ropes to the extent practically possible.
Winch brake pads should be visually checked, and mooring lines should be visually inspected for excessive wear and tear and suitable precautions exercised.
In extreme current and wind conditions, or adverse directions, it should be considered to suspend cargo oil transfer operation and additional payout moorings. Local river and tidal current data and weather forecasts must be monitored, and required information is to be made available for reference.
As a preventive measure, when rough weather or adverse conditions are expected, applying of additional mooring ropes or consideration for suspension / disconnection of cargo operations should be considered.
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