The MARPOL requirements of oil residues (sludge) tanks

Introduction

Oil residue, also known as sludge, refers to the residual waste oil products produced during a ship's routine operations. This includes waste generated from fuel or lubricating oil purification for main or auxiliary machineries, separated waste oil from oil filtering equipment, waste oil collected in drip trays, and waste hydraulic and lubricating oils. Consequently, an oil residue (sludge) tank is a designated compartment that holds such residue, allowing for its disposal either directly through the standard discharge connection or any other approved method.

In accordance with MARPOL/Annex I/Reg. 12, ships with a gross tonnage of 400 and above are mandated to be equipped with a tank or tanks of sufficient capacity. The capacity should be determined with consideration given to the type of machinery and the duration of the voyage, ensuring the proper reception of oil residues (sludge).

Disposal of oil residue (sludge) can be executed directly from the oil residue (sludge) tank(s) to reception facilities via the standard discharge connection (as outlined in regulation 13). Alternatively, disposal may occur through any other approved means, such as an incinerator, auxiliary boiler suitable for burning oil residues (sludge), or other acceptable methods. These approved means should be documented in item 3.2 of the Supplement to the IOPP Certificate Form A or B.

The oil residue (sludge) tank must be equipped with a dedicated pump for transferring its contents and should not feature any discharge connections leading to the bilge system. The only exception is if there is a common piping system leading to the standard discharge connection, which must be facilitated by a check valve (Screw-down non-return). Alternatively, the tank may be outfitted with drains equipped with manually operated self-closing valves, including the subsequent visual monitoring of the settled water.

A designated pump should also be interpreted as any pump that supplies the contents to incinerators or boilers as well as oil residue (sludge) pumps.

Piping to and from oil residue (sludge) tanks shall have no direct connection overboard, other than the standard discharge connection referred to in regulation 13.

The requirements of tanks for oil residues (sludge)

The following requirements shall be subject to the sludge tank of Ships constructed (the keel of the ship is laid or a similar stage of construction) on or after December 1990.

1. Sufficient man-holes shall be provided so that all parts of the tank can be reached to facilitate cleaning.
2. Sludge tanks in ships operating with heavy fuel oil shall be fitted with adequate heating arrangements or other suitable means to facilitate the pumping and discharging of sludge.
3. There shall be no interconnections between the sludge tank discharge piping and the bilge-water piping other than possible common piping leading to the standard discharge connection. However, arrangements may be made for draining of settled water from the sludge tanks by means of manually operated self-closing valves including subsequent visual monitoring of the settled water (Refer to MEPC.1/Circ.753). The check valve (Screw-down non-return) between Bilge pump outlet leading to the standard discharge connection and Sludge pump outlet may be accepted as an independent line (see the Figure 1).

Figure 1 - Common standard shore connection between the sludge system and the bilge system

4. The sludge tank shall be equipped with a designated pump for discharging of the tank contents to reception facilities. The pump shall be of a suitable type, capacity and discharge head. Also, the size and position of the tank and the overall discharge time shall be decided considering the characteristics of the liquid being pumped. Although the pipeline for sludge pump shall be connected directly to a sludge pump, in case of oil residue (sludge) service tank (ie, waste oil tank) that directly supplies oil residue (sludge) to the means of the disposal of oil residue (sludge) on board if this tank is equipped with suitable means of drainage (ie, self-closing valve), it should not be necessary to directly be connected to a sludge pump. In this case, the tank contents may be drained to sludge tank or bilge storage tank through a self-closing valve (U.I MEPC 61/24 Annex 14 was reflected).
5. Moreover, given that oil residues in Scavenge Air drain tank which was designed to store oil residue generated from scavenge air chamber can be transferred by its inner pressure only, no direct connection to sludge pump would be provided. Even though that, this tank shall be listed in paragraph 3.1 of IOPP certificate as an exceptional case.
6. All oil residue (sludge) tanks which meet the requirements of the sludge tank as per item 2 above, regardless of their capacity, shall be entered in this column as follows. But, the tank which is belonged to the bilge system by nature on account of connection to the bilge separator, i.e., M/E Air Cooler Chemical Cleaning Tank, should not be marked with [X] in the para.3.1 of IOPPC even though the subject tank meets all requirements of the sludge tank.
7. Name and capacity of tanks on the certificate shall be made an entry based on Stability Booklet preferentially, in succession Capacity Plan, Sounding Table, Engine Piping Diagram and Manhole cover. Furthermore, Sludge tanks shall be identified by frame numbers and lateral position shall be identified as center, port or starboard.

The requirements on the separation between oily bilge and oil residue systems

The requirement on the separation between oily bilge and oil residues systems has been applied to the ships constructed on or after 31 Dec’ 1990 in accordance with the applicable unified interpretation to MARPOL Annex I, consequently, those amendments will retroactively apply to ships constructed before 31 Dec’ 1990 which oily bilge and oil residue piping arrangements are not separated from each other.

Figure 2 - Acceptable arrangement

Figure 3 – Not acceptable arrangement

Sludge tank capacity

For ships which do not carry ballast water in fuel oil tanks

1) For ships which do not carry ballast water in fuel oil tanks:

V₁ = K₁ x C x D (m³)

K₁:

1. 015 … For ships where heavy fuel oil is purified for main engine use. But, for a ship the keel of which was laid before 31 December 1990, K₁: 0.01
2. 005 … For ships using diesel oil or heavy fuel oil which does not require purification before use.

C: Daily fuel oil consumption (m3)

D: Maximum period of voyage between ports where sludge can be discharged ashore (days). In the absence of precise data, a figure of 30 days shall be used.

2) When such ships are fitted with approved homogenizers, sludge incinerators or other recognized means on board for the control of sludge, the minimum sludge tank capacity shall, in lieu of the above, be:

1. 50 percent of the volume calculated according to para. 1), 0.5 ․V₁ or
2. 1 m³ for ships of 400 GT and above but less than 4,000 GT or 2 m³ for ships of 4,000 GT and above;

Whichever is greater in the above 1) and 2), but, for ships the keel of which was laid before 31 December 1990, the minimum capacity shall be calculated as the above 2).

But, these alleviated requirements on capacity of sludge tanks are applied to the ships where the building contract is placed, or in the absence of a building contract, the keel of which is laid before 1 July 2010, and which are fitted with homogenizers, sludge incinerators or other recognized means on board for the control of sludge, the minimum sludge tank capacity.

For ships which carry ballast water in fuel oil tanks

For ships which carry ballast water in fuel oil tanks, the minimum sludge tank capacity shall be calculated by the following formula:

V₂= V₁+ K₂B (m³)

Where,

V₁= sludge tank capacity specified in the above (a) or (b),

K₂= 0.01 … for heavy fuel bunker tanks, or 0.005 … diesel oil bunker tanks,

B = capacity of ballast water tanks which can also be used to carry fuel oil (ton)