OTM-7.18	Oil Tanker Manual OTM Crude Oil Washing	Doc No.: OTM 7.18 Revision: 01 Date: 15 Oct 2024 Issued by: DPA Approved by: MD

1. APPLICATION

This document applies to Tank vessels managed by Company.

2. PURPOSE

To specify standard requirements for crude oil washing.

3. REQUIREMENT

MARPOL Annex –I, Regulation 33.1- Every new crude oil tanker DWT>20000. For sludge control & heavy weather ballast in cargo tanks.

4. RESPONSIBILITIES

• Master: Seek approval of COW from external parties
• Chief officer: Prepare COW Plan, supervise the operation and ensure compliance with MARPOL requirement
• Deck officers: Responsible officers to assist chief officer
• Watch Keepers: Assist as required

5. GENERAL

Crude oil tankers use crude oil cargo as washing medium if:

• Fitted with approved fixed washing system
• Inert gas system

Crude oil washing is performed either in port or between discharge ports subject to charterer’s permission. Settled sediments are removed and discharged with the cargo. This results in:

• Increased out turn of cargo
• Reduced oil retention, thus less oil is available to cause pollution
• Increased tonnage for the next cargo (more freight earned)
• Reduction in corrosion due to less water washing of the tanks
• Reductions in the time and cost of routine tank cleaning and tank cleaning for dry dock
• Reduced pollution threat when ballasting crude oil washed tanks.
• Less workload of de-sludging prior drydock / repair work
• Reducing damage to pumps and valve seats caused by deposits, and sediment in system.

Recognize dangers associated with crude oil washing & suspend operation in case of:

• Failure of the inert gas system
• Oxygen content exceeds 8% by volume or below terminal requirements
• Cargo tank pressure falls below atmospheric pressure

Note:

• Maintain at least 100 mm WG pressure in tanks.
• Any water content not discharged prior COW
• Leakage from the COW system
• Cargo unsuitable for COW
• Operation is not safe

Pressure test COW system:

• At least annually to 100% of rated working pressure (MAWP- Maximum allowable working pressure)
• 1.5 times the rated working pressure twice within any five-year period

6. PRIOR ARRIVAL

Following required prior arrival:

• Seek Approval from authority and the terminal or vessel in case of STS at least 24 hours in advance

Note:

• Refer to ISGOTT Chapter 11.5- Crude oil washing for more details.
• Perform checks as per “Pre arrival checklist” from approved COW manual
• Pressure test COW system to normal working pressure & repair as required

Note:

• Drain the system after pressure test to avoid leakage due to thermal expansion.
• Verify accuracy of pressure gauges on the line
• Isolate tank cleaning heater from COW line using blanks
• Blank portable washing machine connections
• Close valves & caps on portable washing machine connections
• Ensure routine maintenance of machines done as per PMS
• Prepare COW plan in line with following:
  • Chief Officer to prepare COW plan & include same in discharge plan
  • Plan stages of COW without delaying discharging operation
  • Consider requirements of charterers & COW manual
  • To wash at least one quarter of the tanks for sludge control

  Note:

  • Crude oil wash each tank once in 4 months on rotational basis.
  • To wash sufficient number of tanks to ensure compliance with MARPOL Annex-I for loading heavy weather ballast

Coution:

• Never load heavy weather ballast in tanks not crude oil washed except in case of emergency.
• Multiple cargo grades reduce COW flexibility. Keep following in mind at load port:
  • Plan loading considering COW at discharge port
  • Consider hull stresses, draft & trim at discharge port
  • First discharge slop tank(s) & For COW charge with fresh cargo
  • Load different grades in slop tanks
  • Use same grade for COW to avoid contamination

7. AT BERTH

Verify following prior commencement of COW:

• Tanks under positive pressure
• Oxygen content <8% by volume
• Perform checks as per approved COW manual

During COW operation ensure following:

• Monitor COW system for leaks
• Maintain effective deck watch
• Record all parameters using Form TNK-21
• Use IG system as mentioned in OTM 7.12 Inert Gas System

Warning:

• Suspend COW in case of IG Failure.
• Follow washing sequence as per COW plan
• Trim not less than as mentioned in COW manual
• Pressure not less than as mentioned in COW manual
• Maintain minimum oil level during bottom wash
• To minimize delay simultaneously wash as many tanks as possible
• Maintain required discharge rate during washing
• Every discharging wash slop tanks & tanks used for load on top

Note:

• Discharge tank washings directly ashore, if possible.
• Ensure effective stripping using eductor.
• Drain COW system to ensure following:
  • Improve vessel outturn
  • Reduce damage due to thermal expansion
  • Reduce effect of corrosion
  • Washing lines free of any cargo and ready for water washing
  • Carry out manual sounding to ensure tanks are empty
  • Use Marpol line to discharge final content
  • Use stripper pump to strip/drain lines in pump room

8. REFERENCED FORMS AND CHECKLISTS

• TNK-21- Crude oil washing checklist