Oceangoing Cargo Ships Safety & Operational Matters
Home || Tanker Safety || Container Ship Handling || Commercial Management || EMS ||

Tanker operation : crude oil washing procedure

Crude oil washing (C.O.W.) is a system whereby oil tanks on a tanker are cleaned out between voyages not with water, but with crude oil - the cargo itself. The solvent action of crude oil makes the cleaning process far more effective than when water is used. However, such a technique of washing cargo tanks involves many hazards, and careful consideration will need to be made for safe planning and execution. Preceding operating utmost diligence in planning and execution needs to be made for a safe working environment. The following are the basic guidelines for quick reference. The Chief Officer, as qualified by the requirements as laid down by flag state administration of the ship and any port regulations that may be in force locally, supervise all C.O.W. operations.

containerships operational matters
Oil Tanker Safety Guide

What is Crude oil ? Any liquid hydrocarbon mixture occurring naturally in the earth. Properties of crude oil vary considerably depending upon its origin. Crudes generally have a flashpoint below 26.7 degrees C and a Reid vapor pressure from about 42 to 84kPa. Crude oils have contaminants such as sulfur and vanadium compounds, which encourage corrosion of steel. Crude oils with high and low sulfur contents are referred to as "sour" and "sweet." crude oils respectively.

Supervision Of Crude Oil Washing (COW) Operations

The Chief Officer shall prepare a detailed cargo oil discharge and Crude Oil Washing Plan before the arrival discharge port. He shall carry out the operations following the plan. Reference should also be made to the latest I.M.O.s publication Crude Oil Washing Systems and I.C.S./OCIMFs publication- the ISGOTT. The Master, Chief Officer, Chief Engineer and other officers engaged in Crude Oil Washing shall be fully familiar with the crude oil washing system provide on board the vessel.

If the Chief Officer is less experienced, the qualified Master shall assist in the supervision of the operations. He shall be knowledgeable about the contents of the Operations and Equipment Manual.


Discharging Strategy : The discharge sequence is to be such that the vessel has a good draining trim at an early stage in the discharge. It will allow early active operations. When planning for C.O.W., the frequency and time of removing the cargo pumps from discharge operations should be planned for minimum, for efficient discharge. Under no circumstances are Crude Oil Washing operations to be commenced without operational inert gas equipment. Any Butterworth tank washing water heaters fitted must be blanked off and drained at all times. Before each Crude Oil Washing operation, a full pressure test of the system must be carried out. The procedures and instructions contained in the vessels Crude Oil Washing Operations and Equipment Manual must be strictly adhered to.

Terminal (Refinery) request : Special details, port requirements and special precautions or procedures should be discussed with all personnel involved in the discharge operation. (eg. any special requirements for final discharge of crude (Fresh or Dirty) prior to completion of discharge operations, etc)

COW Manual: Crude Oil Washing and related operations shall be carried out under the Operations and Equipment manuals (C.O.W. manuals) approved by the class on behalf of flag state Government and provided onboard each ship.

Advance Notice In Port: Where it is required to carry out crude oil washing during cargo discharge, the Master should inform the terminal and seek terminals' permission. The same shall be discussed in detail before the start of cargo operations in the Pre cargo transfer safety meeting held with the terminal. C.O.W. should proceed, only after terminals, permission is granted. For crude oil washing carried out in Japanese ports, the Master shall obtain approval of the Charterer, consignee, unloading terminal, harbormaster and others.

Safety Measures For Crude Oil Washing Operations

For crude oil washing, the Chief Officer shall carry out the following safety matters and observe the safety regulations on crude oil washing provided by the terminal (if any). Some terminals require the vessel to complete the terminal-specific safety Questionnaire / Permit / Checklists before granting permission for approval. He shall also follow the safety precautions as laid in the relevant section of the Latest version of ISGOTT. The following shall be not used and isolated before carrying C.O.W.:
  1. Between tank cleaning lines and overboard discharge or Engine Room
  2. Tank Cleaning Heaters (to be blanked)
  3. Overboard Discharge Lines (to be isolated)
  4. Portable Washing Machines (not to be used for C.O.W. and their hydrants blanked)
  5. Cargo Sea Chests (to be blanked)

Pressure Test before Arrival Port: Conduct a pressure test of C.O.W. lines before arrival. Any leakages must be rectified and the system, re-tested to be proved leak-free.

Confirming Atmosphere in Tanks to be Crude Oil Washed
  1. Before the commencement of C.O.W., operations ensure that the oxygen content of the cargo oil tanks being washed is below 8%. Refer to Cargo Oil Tank Oxygen & H2S monitoring Record for Voyage of Double Hull Operation and Oil Tank Monitoring Record.
  2. During C.O.W. operations ensure that the cargo oil tank pressure is minimum 200 mmAq and that the I.G.S. produces inert gas with an oxygen content of less than 5%.
  3. For Prevention of Electrostatic Generation Do not use crude oil containing water, as washing oil.

Note: Mixtures of crude oil and water can produce electrically charged mist, during washing with an electrical potential considerably above that produced by Dry crude. Refer to the relevant section in ISGOTT for precautions for Static Electricity generation and its hazards. Before using such oil as a source of crude oil for washing, any water settled down during the voyage must be De-bottomed (by discharging) to terminal by at least one meter in depth. Where load-on-top method has been used for cargo in slop tank (previously containing oily water mixtures), the whole cargo oil in that slop tank which needs to be used as a source of oil for crude oil washing must be discharged ashore and then refilled with fresh crude from other tanks.

Communication equipment: Ensure only intrinsically portable radios are used on deck during C.O.W. operations. Deck crew shall be in prompt communication with the Duty officer & chief officer.

Suspending Crude Oil Washing: Suspend COW operations immediately if:
Prevention Of Air Pollution : Follow the Precautions Against Air Pollution to minimize petroleum vapor emissions.

Crude Oil Washing Plan: The Chief Officer shall prepare a detailed C.O.W. plan following the Crude Oil Washing Plan to carry out the C.O.W. operation most safely and efficiently. Before the arrival of the Port, or at the earliest opportunity after that, the Chief Officer shall conduct a Pre transfer cargo safety meeting with all personnel involved in the C.O.W. operation to ensure that all have read and fully understand the plan.

Personnel Arrangement For Operations: Carry out Crude Oil Washing by the adequate personnel arrangement as per C.O.W. plan under the reference of the Personnel Arrangement for Crude Oil Washing

Points Of Crude Oil Washing: C.O.W. operations shall always be carried out following the Crude Oil Washing Operations. C.O.W. operations for High Viscosity & High Pour point (Heated) cargoes shall always be carried out under the Crude Oil Washing of Heated Cargo


The Chief Officer should ensure that the following records are kept during COW operations:
  1. Crude oil washing check list
  2. Oil record book: According to the Procedures for Entry in Oil Record Book
  3. Deck logbook: Date and time, and results of a C.O.W. line pressure test and operation test of related equipment.
  4. Crude Oil Washing Record
  5. Cargo Oil Tank Oxygen & H2S monitoring Record for Voyage of Double Hull Operation and Oil Tank Monitoring Record: It is the Measurement record of oxygen level in tanks Before entering Load port, before entering the cargo, Before entering discharge port and Before crude oil washing.
  6. Inert gas record : Log for four hourly I.G. pressure monitoring of cargo tanks, in addition to Continuous pressure recording by the fixed recorder of I.G.S. mainline pressure after loading, until completion of discharge.

Ships Fitted with Fixed Foam Systems

In ships fitted with fixed foam systems, the Chief Officer will satisfy himself that the system is fully operational before commencing cargo, C.O.W., or tank cleaning operations. A fire hose and jet/spray nozzle must be placed alongside, connected to the fire main.

Regulations For Reference

MARPOL 73/78 Convention, ANNEX I
Lawson Prevention of Marine Pollution and Sea Disasters (Japan) OPA90, C.F.R. (U.S.)

Documents For Reference

IMO-Crude Oil Washing System, (Latest edition)
IMO-Inert Gas System, Latest edition
ICS / OCIMF - International Safety Guide for Oil Tankers and Terminal (ISGOTT) (Latest edition)

Related topics:

Oil pollution control method

Gas freeing arrangement for oil tanker

Handling guideline for oil cargo

Oil pollution prevention method

Preparation for loading oil cargo

How to prevent spillage of oil cargo

General precautions for oil cargo loading in tankers

General precautions for tankers

General guidances for tank cleaning

General precautions for ballasting procedure

Tanker operation in a laden voyage

Preparation for discharging oil cargo

General precautions for oil cargo discharging

Related articles

Safety practice for crude oil washing onboard oil tankers
Oil tanker operations - tank cleaning,purging & gas freeing

Safety checks prior discharging sludge from ship to reception facilities

Bulk liquid cargo handling - Ship to shore safety checklist

Ship-to-ship transfer / Operational guideline and check item for oil tankers

General precautions for tankers

Safety precautions prior transferring oil

Reporting oil spillage in foreign ports

How to use low sulphur fuel oil onboard

Operational guideline during bunkering

Fuel oil sulpher quantity frquently asked questions

What is fuel oil additive ?

Guideline for Proper heating of Fuel Oil storage tank

Dealing with low quality fuel oil

What is the procedure for fuel oil viscosity control ?

How to keep a sample of fuel oil received ?

How to keep bunkering record ?

Procedure for receiving lub oil

Precautions prior transferring fuel oil into storage tanks

Ships bunkering guideline- planning, preparation, safety checks & confirmation

Safety precautions prior transferring oil

Bunkering arrangement and safety factors onboard

Bunkering safe procedure and detail guideline for ships

What is fuel oil additive ?

Dealing with low quality fuel oil

How to keep a sample of fuel oil received ?

How to keep bunkering record ?

Acceptance / rejection of fuel in a quality dispute

Precautions prior transferring fuel oil into storage tanks

Requirement of towing arrangement in oil tankers, readyness, & training onboard

How to deal with ships power failure ? ....

Other info pages !

Ships Charterparties Related terms & guideline
Stevedores injury How to prevent injury onboard
Environmental issues How to prevent marine pollution
Cargo & Ballast Handling Safety Guideline
Reefer cargo handling Troubleshoot and countermeasures
DG cargo handling Procedures & Guidelines
Safety in engine room Standard procedures
Questions from user and feedback Read our knowledgebase
Home page

ShipsBusiness.com is merely an informational site about various aspects of ships operation,maintenance procedure, prevention of pollution and many safety guideline. The procedures explained here are only indicative, not exhaustive in nature and one must always be guided by practices of good seamanship.

User feedback is important to update our database. For any comment or suggestions please Contact us
Site Use and Privacy - Read our privacy policy and site use information.
//Home //Terms and conditions of use

Copyright © 2015 www.shipsbusiness.com All rights reserved.