Tank Cleaning
Crude Oil Washing applicability follows MARPOL Annex I criteria, certificates and the approved manual; it does not arise from generic tanker size or the informal presence of an equivalent system.
Operational Explanation
Tank cleaning varies significantly depending on ship and cargo type: on tankers, Crude Oil Washing (COW) uses the crude oil itself as the washing agent to reduce oily residues; on chemical tankers, washing is specific to the NLS substance carried, according to the P&A Manual, and is often a prerequisite for the next cargo (to avoid contamination between different products).
In both cases, the main risk is not technical but documentary and procedural: a wash carried out correctly but not adequately recorded, or carried out using a procedure that does not conform to the ship's specific manual, still generates a deficiency during inspection.
Regulatory Reference
MARPOL Annex I Regulations 18, 33 and 35. Regulation 33 covers every crude oil tanker of 20,000 DWT and above delivered after 1 June 1982. Regulation 18.7 addresses certain crude oil tankers of 40,000 DWT and above delivered on or before that date operating COW in lieu of segregated ballast tanks, except where crude is unsuitable. Equivalence only when formally accepted by the Administration.
Scope of Application
Check IOPP Certificate and Supplement, approved COW Operations and Equipment Manual, delivery date, DWT, trade and Administration requirements. Where COW is required, operate it under Regulation 35 and the approved manual.
Procedure / How to Complete It
- Determine applicability from IOPP Certificate/Supplement and ship particulars.
- Check the approved COW Operations and Equipment Manual and crude suitability.
- Conduct COW under Regulation 35, the manual and ship checklist.
- Use an equivalence only when formally accepted by the Administration and documented.
- Record operations in the applicable record books.
Practical Example
Example on a chemical tanker: washing of tank no. 2 after discharging methanol, according to the specific procedure in the P&A Manual, with verification of the absence of residues before loading the next product, which is incompatible with residual traces of methanol.
What Typically Goes Wrong
Common Mistakes Mistake Library
| Mistake | Consequence | How to avoid it |
|---|---|---|
| Generic washing procedure applied instead of the specific one in the P&A Manual | Residues not adequately removed, risk of contamination | Always consult the P&A Manual specific to the combination of products involved |
| COW carried out without respecting the pressure or sequence specified in the COW Manual | Reduced washing effectiveness, oily residues higher than expected | Rigorously follow the parameters of the approved COW Manual |
| Incomplete or generic recording of the wash | PSC deficiency, difficulty demonstrating compliance in case of a dispute | Record every stage in detail (tank, quantity, destination of residues, time) |
What the PSCO Checks
Operational Tips
- Always consult the specific P&A Manual before every wash, especially with unusual product sequences.
- Do not depart from the pressure and sequence parameters of the COW Manual to save time.
- Record every stage of the wash in full detail, not just the final outcome.
Preparation checklist
- IOPP Certificate and Supplement checked
- Delivery date and DWT compared with Regulations 18 and 33
- Approved COW Manual available
- Crude suitability checked
- Any equivalence formally accepted and documented
FAQ
Related Topics
Last substantive revision of this page: 31 August 2026 · page fingerprint fc9fa5d46aee