M77

M77
M77(Sep2016)(cont)(Rev.1Aug 2019)(Rev.2Dec 2020)(Rev.3
Sep 2021)(Rev.4Feb 2023)

Storage and use of SCR reductants
1.

GeneralThe NOx Technical Code, in 2.2.5 and elsewhere, provides for the use of NOx Reducing
Devices of which Selective Catalytic Reduction (SCR) is one option. SCR requires the use ofa reductant which may be a urea/water solution or, in exceptional cases, aqueous ammonia
or even anhydrous ammonia. These requirements apply to the arrangements for the storage
and use of SCR reductants which are typically carried on board in bulk quantities.
The requirements for SCR reductants tanks with volume below of 500 L are left to thediscretion of individual Classification Societies. This discretion is only applicable to Section 2of the UR.
Note:
1. This UR is to be uniformly implemented by IACS Societies for the storage tank of SCR
reductants:i) when an application for installation, i.e. submission date of plans, is made on or after 1
January 2018; orii) which is installed in ships contracted for construction on or after 1 January 2018.
2. The “contracted for construction” date means the date on which the contract to build thevessel is signed between the prospective owner and the shipbuilder. For further details
regarding the date of “contract for construction”, refer to IACS Procedural Requirement(PR) No. 29.
3. Rev. 1 of this UR is to be uniformly implemented by IACS Societies for the storage tank ofSCR reductants:i) when an application for installation, i.e. submission date of plans, is made on or after 1January 2021; orii) which is installed in ships contracted for construction on or after 1 January 2021.
4. Rev.2 of this UR is to be uniformly implemented by IACS Societies for the storage tank ofSCR reductants:i) when an application for installation, i.e. submission date of plans, is made on or after 1
January 2022; orii) which is installed in ships contracted for construction on or after 1 January 2022.
5. Rev.3 of this UR is to be uniformly implemented by IACS Societies for the storage tank ofSCR reductants:i) when an application for installation, i.e. submission date of plans, is made on or after 1
July 2022; orii) which is installed in ships contracted for construction on or after 1 July 2022.
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6. Rev.4 of this UR is to be uniformly implemented by IACS Societies for the storage tank ofSCR reductants:i) when an application for installation, i.e. submission date of plans, is made on or after 1
January 2024; orii) which is installed in ships contracted for construction on or after 1 January 2024.

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2.

Reductant using urea based ammonia (e.g. 40%/60% urea/water solution)

2.1 Where urea based ammonia (e.g. AUS 40 – aqueous urea solution specified in ISO
18611-1:2014) is introduced, the storage tank is to be arranged so that any leakage will becontained and prevented from making contact with heated surfaces. All pipes or other tankpenetrations are to be provided with manual closing valves attached to the tank. Tank andpiping arrangements are to be approved.
2.2

The storage tank may be located within the engine room.

2.3 The storage tank is to be protected from excessively high or low temperatures
applicable to the particular concentration of the solution. Depending on the operational areaof the ship, this may necessitate the fitting of heating and/or cooling systems. The physicalconditions recommended by applicable recognized standards (such as ISO 18611-3:2014)
are to be taken into account to ensure that the contents of the aqueous urea tank aremaintained to avoid any impairment of the urea solution during storage.
2.4 If a urea storage tank is installed in a closed compartment, the area is to be served byan effective mechanical ventilation system of extraction type providing not less than 6 airchanges per hour which is independent from the ventilation system of accommodation,
service spaces, or control stations. The ventilation system is to be capable of being controlledfrom outside the compartment. A warning notice requiring the use of such ventilation before
entering the compartment shall be provided outside the compartment adjacent to each pointof entry.
Alternatively, where a urea storage tank is located within an engine room a separate
ventilation system is not required when the general ventilation system for the space isarranged so as to provide an effective movement of air in the vicinity of the storage tank andis to be maintained in operation continuously except when the storage tank is empty and has
been thoroughly ventilated.
2.5 Each urea storage tank is to be provided with temperature and level monitoringarrangements. High and low level alarms together with high and low temperature alarms arealso to be provided.
2.6 Where urea based ammonia solution is stored in integral tanks, the following are to beconsidered during the design and construction:•These tanks may be designed and constructed as integral part of the hull, (e.g. doublebottom, wing tanks).

•These tanks are to be coated with appropriate anti-corrosion coating and cannot belocated adjacent to any fuel oil and fresh water tank.

•These tanks are to be designed and constructed as per the structural requirements
applicable to hull and primary support members for a deep tank construction.

•These tanks are to be included in the ship’s stability calculation.

2.7 The requirements specified in M77.2.4 also apply to closed compartments normallyentered by persons:•when they are adjacent to the urea integral tanks and there are possible leak points(e.g. manhole, fittings) from these tanks; orPage 3 of 4

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when the urea piping systems pass through these compartments, unless the piping
system is made of steel or other equivalent material with melting point above 925
degrees C and with fully welded joints.

2.8 The reductant piping and venting systems are to be independent of other ship service
piping and/or systems. Reductant piping systems are not to be located in accommodation,
service spaces, or control stations. The vent pipes of the storage tank are to terminate in asafe location on the weather deck and the tank venting system is to be arranged to prevent
entrance of water into the urea tank.
2.9 Reductant tanks are to be of steel or other equivalent material* with a melting point
above 925 degrees C.
Pipes/piping systems are to be of steel or other equivalent material with melting point above
925 degrees C, except downstream of the tank valve, provided this valve is metal seated andarranged as fail-to-closed or with quick closing from a safe position outside the space in theevent of fire; in such case, type approved plastic piping may be accepted even if it has notpassed a fire endurance test. Reductant tanks and pipes/piping systems are to be made witha material compatible with reductant or coated with appropriate anti-corrosion coating.
2.10 For the protection of crew members, the ship is to have on board suitable personnel
protective equipment. Eyewash are to be provided, the location and number of theseeyewash stations are to be derived from the detailed installation arrangements.
2.11 Urea storage tanks are to be arranged so that they can be emptied of urea andventilated by means of portable or permanent systems.
3.

Reductant using aqueous ammonia (28% or less concentration of ammonia)

Aqueous ammonia is not to be used as a reductant in a SCR except where it can bedemonstrated that it is not practicable to use a urea based reductant. Where an application ismade to use aqueous ammonia as the reductant then the arrangements for its loading,carriage and use are to be derived from a risk based analysis.
4.
Reductant using anhydrous ammonia (99.5% or greater concentration ofammonia by weight)
Anhydrous ammonia is not to be used as a reductant in a SCR except where it can bedemonstrated that it is not practicable to use a urea based reductant and where the Flag
Administration agrees to its use. Where it is not practicable to use a urea reductant then it isalso to be demonstrated that it is not practicable to use aqueous ammonia. Where anapplication is made to use anhydrous ammonia as the reductant then the arrangements for its
loading, carriage and use are to be derived from a risk based analysis.
* Footnote to 2.9: Material requirement “to be of steel or other equivalent material” in the first paragraph with amelting point above 925 degrees C is not applicable for integral tanks on FRP vessels such as those listed below,
provided that the integral tanks are coated and/or insulated with a self-extinguishing material.
1) FRP vessels complying with Regulation 17 of SOLAS Chapter II-2 based upon its associated IMO guidelines(MSC.1/Circ.1574), and2) FRP vessels exempted from the application of SOLAS e.g., yachts, fast patrol, navy vessels, etc., generally ofless than 500 gross tonnage, subject to yacht codes or flag regulations.

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