Operational guide · Operational procedure

Tank Cleaning

Tank cleaning requires three distinct checks: environmental handling of washing and residues, operational safety, and suitability for the next cargo. The MARPOL regime, P&A Manual or Crude Oil Washing (COW) manual, SMS procedures and acceptance criteria determine the checks and records needed for the particular case.

tank cleaningCOWMARPOL Annex IMARPOL Annex II

Operational Explanation

Separate three objectives: environmental compliance of washing and residues, operational safety, and tank suitability for the next cargo. The P&A Manual addresses MARPOL Annex II: it is not a complete safety guide and does not by itself guarantee commercial cleanliness.

COW uses crude oil to remove oily residues under the approved manual. For a product change, also assess safety information, coating and equipment compatibility, SMS procedures and documented next-cargo requirements.

Regulatory Reference

MARPOL Annex I — MEPC.117(52) — regs. 18, 33, 35–36; MARPOL Annex II — MEPC.118(52) — regs. 13–15, Appendix 4; MEPC.315(74) — persistent floaters. Apply the texts with relevant amendments. For COW, check the Convention delivery definitions and certificates; a generic commercial delivery date is insufficient.

Scope of Application

COW: check IOPP/Supplement, DWT and MARPOL definitions; regulation 33 concerns crude oil tankers from 20,000 DWT delivered after 1 June 1982, with a separate regulation 18.7 case for certain earlier ships from 40,000 DWT. NLS: identify substance, category, prewash and residue handling in the P&A Manual, including persistent floaters where applicable.

Procedure / How to Complete It

Determine the Annex I or II regime and applicable manuals; for COW also check crude suitability.
Assess washing risks under the SMS and product information; verify equipment, isolation and prescribed operating conditions.
Plan residue collection and destination and any required prewash; do not treat wash water as freely dischargeable.
Separately confirm next-cargo acceptance criteria and required checks; washing does not authorize tank entry.
Record applicable Annex I operations in ORB Part II or Annex II operations in the Cargo Record Book.

Practical Example

After methanol discharge, the Company checks Annex II obligations and defines preparation consistent with the next cargo, coatings and safety instructions. Commercial acceptance uses agreed criteria and checks: completing the P&A Manual procedure alone does not prove absence of contaminants.

What Typically Goes Wrong

Confusing environmental prewash with commercial cleaning, or treating a washed tank as automatically safe for entry. Verify the three objectives and required evidence separately.

Common Mistakes Mistake Library

Mistake	Consequence	How to avoid it
Using the P&A Manual as the sole safety guide or guarantee of next-cargo purity	Washing risks or residual contamination are not assessed	Separate the MARPOL check, risk assessment and safety instructions, and next-cargo criteria and checks
Changing COW pressure or sequence outside the approved manual	Operation falls outside the conditions prescribed for the system	Follow the COW manual and check prescribed conditions before and during washing
Recording washing without documenting residue destination under the applicable regime	The residue route and compliance of disposal cannot be reconstructed	Plan the permitted destination and record operations and transfers in the relevant book, linking the required evidence

What the PSCO Checks

For Annex I: IOPP/Supplement, COW Manual and ORB Part II. For Annex II: relevant certificate, P&A Manual, Cargo Record Book, prewash and disposal evidence where required. Documentary compliance does not replace safe operating conditions.

Operational Tips

Agree the objective, procedure, residue destination and acceptance criteria before washing.
Apply enclosed-space entry procedures to any entry: washing does not mean gas-free.

Preparation checklist

Annex I/II regime and certificates checked
Applicable manuals and operating risks checked
Prewash and residue destination determined
Next-cargo criteria confirmed separately
Relevant record book identified

FAQ

Is COW mandatory on every tanker?

No. Regulation 33 requires it for every crude oil tanker of 20,000 DWT and above delivered after 1 June 1982; Regulation 18.7 has a distinct branch for certain crude oil tankers of 40,000 DWT and above delivered on or before that date.

Does another system automatically replace COW?

No. An equivalence must be formally accepted by the Administration under the Convention.

How is the actual case checked?

Against the IOPP Certificate/Supplement, approved COW Manual and Administration requirements.

Does a MARPOL prewash make the tank ready for the next cargo or for entry?

No. Prewash addresses the applicable environmental requirements. Suitability for the next cargo and safety of any entry require separate assessments, procedures and checks; the P&A Manual is neither a complete safety guide nor a guarantee of commercial cleanliness.