Sludge Management
Oil-residue collection and disposal, weekly inventory and consistency between tanks, ORB and receipts.
Operational Explanation
"Sludge" is the oily residue produced mainly by fuel and lubricating oil purifiers, and to a lesser extent by drainage and leakage in the machinery space. It must be collected in dedicated tanks, recorded in the Oil Record Book (code C) and disposed of to a port reception facility or by any other approved means — an incinerator, an auxiliary boiler suitable for burning oil residues, or other acceptable means. Disposal ashore uses the standard discharge connection under regulation 13. Other means of disposal must be approved and recorded in item 3.2 of the IOPP Certificate Supplement, Form A or B; this item is not a requirement to list the reception facility.
It is not Regulation 16 of Annex VI that governs the incineration of the ashes: Regulation 16 governs the incineration of sludge, that is the process and its emissions to air. The ashes that come out are Annex V garbage, which names them by definition.
Regulation 12 distinguishes two piping prohibitions. Paragraph 12.3.3 concerns connections to the bilge system, oily bilge water holding tanks, tank top and separators, with specific exceptions. Paragraph 12.3.4 prohibits direct overboard connections other than the regulation 13 standard discharge connection. Check both in the ship’s approved arrangement.
The numbering used here follows regulation 12 as replaced by MEPC.266(68), in force since 1 January 2017.
Regulatory Reference
MARPOL Annex I, Regulation 12 (Tanks for oil residues (sludge)): in the version replaced by resolution MEPC.266(68), in force since 1 January 2017. Oil residue tanks must be of adequate capacity (12.3.1), fitted with a designated pump able to take suction from them (12.3.2), and built so as to facilitate their cleaning (12.3.5). The two piping prohibitions are two, distinct, and must be read together. 12.3.3 looks inboard: the tanks “shall have no discharge connections to the bilge system, oily bilge water holding tank(s), tank top or oily water separators”, with two exceptions only — drains with manually operated self-closing valves and subsequent visual monitoring of settled water, leading to an oily bilge water holding tank or bilge well, or an alternative arrangement that does not connect directly to the bilge discharge piping system; and a common piping leading to the standard discharge connection of Regulation 13, provided it does not allow the transfer of sludge to the bilge system. 12.3.4 looks outboard: the tanks “shall not be arranged with any piping that has direct connection overboard, other than the standard discharge connection referred to in regulation 13”. It is the provision a magic pipe breaches. Ships constructed before 1 January 2017 had to comply with 12.3.3 by the first renewal survey on or after that date. Regulation 17 (ORB entry code C — collection and disposal of oily residues). For the on-board incineration of sludge: Annex VI Regulation 16. The resulting ashes are not an Annex VI matter: they are garbage under Annex V, which at Regulation 1 defines “incinerator ashes” as “ash and clinkers resulting from shipboard incinerators used for the incineration of garbage” and includes them in the definition of garbage (res. MEPC.201(62)).
Scope of Application
Annex I Regulation 12, unless indicated otherwise, applies to ships of 400 gross tonnage and above fitted with combustion machinery that generates oily residues (main and auxiliary engines, HFO/MDO/LO purifiers). Below that threshold obligations may still exist, but they come from elsewhere: flag requirements, approved equipment fitted on board, the company SMS or local rules.
Procedure / How to Complete It
- Identify IOPP Supplement sludge tanks and complete weekly C11.1–11.3 capacity and retained quantity.
- Operator-initiated manual collection: applicable C11.1–11.4 fields. Disposal/transfer: C12.x without tank capacity.
- Use only regulation 12 permitted and approved piping/arrangements; no sludge-to-bilge transfers outside them.
- Dispose to a reception facility through the regulation 13 standard discharge connection, or use another approved means recorded in item 3.2 of the IOPP Supplement; retain delivery receipts. For combustion check equipment and local restrictions: ECA status is not itself an incineration prohibition.
- Record without delay and sign. Additional daily/monthly balances follow the SMS and do not replace weekly C11.
Diagram: sludge balance (input/output)
Practical Example
Weekly ORB C 11.1–11.3 inventory: for each sludge tank in the IOPP Supplement, identification, capacity in m³ and quantity retained in m³. Training example, no disposals: 07-SEP-2026, tank S1, capacity 10 m³, retained 2 m³; 14-SEP-2026, same tank and capacity, retained 2.8 m³. Each inventory signed by the officer in charge. This is not the SMS monthly balance and does not impose the same weekly inventory on bilge tanks. MEPC.1/Circ.736/Rev.2, examples 1–2; MEPC.187(59), C11.
The supplementary balance reconciles opening stock, collections/production, disposals and closing stock. Frequency and investigation thresholds are set in the SMS according to calibration and measurement; 0.1 m³ is not a universal tolerance.
What Typically Goes Wrong
Common Mistakes Mistake Library
| Mistake | Consequence | How to avoid it |
|---|---|---|
| Sludge balance with a large, unexplained variance | Suspicion of illegal discharge, in-depth investigation | Weekly C11 inventory; additional SMS balances and reconciliation with fuel consumption |
| Internal tank-to-tank transfers not recorded | Inconsistency in ORB volumes | Record every internal transfer as a code C entry |
| Disposal without a Waste Delivery Receipt | Unable to prove proper disposal | Always keep the reception facility's receipt |
What the PSCO Checks
Operational Tips
- Supplement the weekly inventory with any SMS-defined balances.
- Record transfers and disposals under applicable items and approved arrangements.
- Retain receipts and explain variances.
Preparation checklist
Educational checklist. This summary supports learning and preparation only. It does not replace the vessel’s approved procedures, manuals, statutory documents, company SMS, or applicable official requirements. Completing it demonstrates neither compliance nor readiness for an inspection: it shows that a list has been read, not that the ship is in order. Always verify the current documents carried on board.
- Weekly C11 present also in weeks without disposal.
- Manual C11.4 distinguished from inventory and C12.
- Receipts, signatures and quantities consistent; any company balance follows SMS.
- Approved disposal method usable in the area.
FAQ
Related Topics
Last substantive revision of this page: 15 September 2026 · page fingerprint 25a846044555