Tuesday, June 25, 2013

COW: Crude Oil Washing..All Know Hows Compiled!


COW: Crude Oil Washing

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MANDATE UNDER MARPOL ANNEX 1 REG 13

Points to Remeber:
    oil tanker cow cleaning
  1. Vessel must have certified COW system and COW manual.
  2. Personnel trained for its operation.
  3. It must be carried out while vessel is discharging cargo.
  4. Use of high pressure jets of cargo itself to be used @ 9-10 bar pressure through nozzle sprays.
  5. Each nozzle rotates at 120 deg.
  6. IG system to be used simultaneously and O2 level to maintain below 5-8%.
  7. The spray jets are permanently positioned tank cleaning nozzles must be employed and the jets move down as discharging carries on.
  8. The COW ops must be synchronized with the cargo discharging so that oil below the steam pipes does not solidify upon cooling.
  9. Tank cleaning can be carried out even at temperatures as low as 5 deg above the pour point.  
  10. For tankers carrying the same cargo throughout the contract, still must be washed by COW at least every 4 months.
  11. If water ballast needs to be carried in the cargo tank then COW the tank and then rinse with the water.
  12. Water so collected must be stored in the slop tank and care must be taken while discharging it to shore facility.
  13. COW must be completed before leaving port, never do it en-route.
  14. Dirty Water Ballast entry must be made in the ORB-2 (Oil Record Book).
  15. All entries regarding the COW ops and ballast/deballast to be entered into ORB-2.
tanker cross section

Precautions during COW
(courtesy: marineinsight.com)
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

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