COW: Crude Oil Washing
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MANDATE UNDER MARPOL ANNEX 1 REG 13
Points to Remeber:
- Vessel must have certified COW system and COW manual.
- Personnel trained for its operation.
- It must be carried out while vessel is discharging cargo.
- Use of high pressure jets of cargo itself to be used @ 9-10 bar pressure through nozzle sprays.
- Each nozzle rotates at 120 deg.
- IG system to be used simultaneously and O2 level to maintain below 5-8%.
- The spray jets are permanently positioned tank cleaning nozzles must be employed and the jets move down as discharging carries on.
- The COW ops must be synchronized with the cargo discharging so that oil below the steam pipes does not solidify upon cooling.
- Tank cleaning can be carried out even at temperatures as low as 5 deg above the pour point.
- For tankers carrying the same cargo throughout the contract, still must be washed by COW at least every 4 months.
- If water ballast needs to be carried in the cargo tank then COW the tank and then rinse with the water.
- Water so collected must be stored in the slop tank and care must be taken while discharging it to shore facility.
- COW must be completed before leaving port, never do it en-route.
- Dirty Water Ballast entry must be made in the ORB-2 (Oil Record Book).
- All entries regarding the COW ops and ballast/deballast to be entered into ORB-2.
Precautions during COW
Before starting the operation
- Confirm all pre arrival checks are performed
- The complete COW operation to be discussed with ship and shore staff
- Set a communication channel between ship and shore facility for COW operation-Ship shore interface
- Signal and Emergency signs to be discussed to stop the operation between shore and ship staff
- Inert Gas plant to be working and oxygen content must be less than 5 %
- Fixed Oxygen analyser to be checked and calibrated for proper functioning
- Portable oxygen analyser should be made available and checked for proper functioning.
- Oxygen reading in swash bulkhead tanks must be taken from both the sides
- All tanks must be checked for positive inert gas pressure
- Assign duties to all responsible ship staff. One person to be assigned to check the leakage in the pipe line system as soon as the operation starts
- Check all the equipments under COW system for proper functioning
- Check and Set the line and valves for ship to shore under COW system
When the operation is under process
- The inert gas values to be frequently checked- Tank pressure and O2 value
- The crude oil washing must be done in the designated tanks as per the plan including the washing cycle
- A responsible person to be always present on deck
- All deck lines and valves must be frequently checked for any leakages
- Parameters and running condition of all the machineries involved in operation to be frequently checked
- Ullage gauge floats to be raised for the tanks which are being washed
- Trim should be sufficient to assist the bottom washing of tanks
- The level of holding tanks to be continuously monitored to avoid overflow
When the Operation is finished
- Drain tank wash line off crude oil
- Shut all the valves in the line used for the operation
- Stop and drain all the machines involved in the operation
- Drain all the cargo pumps after the operation is finished