Tank Cleaning
From Crude Oil Washing on tankers to chemical washing on chemical tankers: different procedures for different risks, but one common principle — accurate recording of every stage.
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, Regulation 33 (Crude Oil Washing, mandatory on tankers meeting the applicable requirements) and MARPOL Annex II with the ship's specific P&A Manual for NLS tank cleaning.
Scope of Application
Tankers subject to COW under MARPOL Annex I Regulation 33; chemical tankers for NLS tank cleaning under their own approved P&A Manual.
Procedure / How to Complete It
- For tankers: carry out Crude Oil Washing according to the ship's approved COW Manual, checking pressure, number of tank-washing machines and the sequence specified.
- For chemical tankers: identify the specific washing procedure for the NLS substance just discharged, according to the P&A Manual, before proceeding.
- Check the compatibility between the previous product and the one to be loaded next, to avoid cross-contamination.
- Record every stage of the wash (start, end, quantity of residues, destination) in the appropriate record book (Oil Record Book or Cargo Record Book).
- Where required, verify the tank's actual cleanliness through visual inspection or specific tests before the next loading.
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.
Real Cases
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) |
PSC Observations
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.
Checklist
- Specific washing procedure identified (COW Manual or P&A Manual)
- Compatibility between the previous and next product verified
- Washing parameters (pressure, sequence) respected
- Every stage recorded in the appropriate record book
- Actual cleanliness verified before the next loading, where required