Fuel Oil - Treat it Right

North continues to see incidents where engine damage has been caused or alleged to have been caused by the presence of excessive cat fines in the fuel. In a number of these cases, cat fine damage resulted from fuel that was tested and found to be within bunker specification.

The damage to an engine that can be caused by cat fines in the fuel oil is well documented. The aluminium and silicon fines, carried over into the fuel as a result of the catalytic cracking process during refining, act as an aggressive abrasive and, if in sufficient concentrations, can lead to rapid wear of engine components.

The allowable concentration of cat fines in marine fuels is limited by the international standard ISO 8217 “Specifications of Marine Fuels”. The fifth, and current, edition was
released in 2012 and sets the maximum concentration of combined aluminium and silicon fines at 60mg/kg for the most commonly used residual fuels RMG 180 and RMG 380.

A failure to properly operate and maintain the vessel’s fuel treatment equipment and systems can lead to bunkers that were supplied “onspecification” in accordance with charterparties causing significant damage to engine components. If the fuel was provided by the charterer  nd was found to comply with ISO 8217, it would be very difficult for an owner to hold the  harterer liable for the damage.

Fuel containing 60mg/kg of cat fines may be within specification but it is highly unlikely that such levels will be suitable for the engine. In fact, the concentration of cat fines may actually increase whilst in the vessel’s storage tanks as they gravitate towards the bottom of the tanks.

The maximum allowable concentration at injection will be specified by the engine manufacturer and is usually around 15mg/kg. In most cases this will require some form
of fuel treatment.

Ensuring the ship’s engineers receive the bunker fuel laboratory analysis results as soon as they are available will help them take the prompt and proper action needed to treat the fuel and prevent damaging levels of cat fines reaching the engines. It is important to note that an absence of a caution or alert on the lab analysis report does not mean any less care can be taken when treating the fuel on board.

Fuel treatment on board a vessel broadly consists of three methods:

1. regular draining of water and sludge from the settling tank(s)
2. centrifugal separation between the settling and service tanks, and
3. fuel system in-line filtration.

Perhaps the most effective method of lowering the concentration of cat fines in the fuel is through the proper use of the ship’s centrifugal separators. Different ships may have different equipment and arrangements, such as traditional purifiers in parallel, in a purifier-clarifier train or as a standalone “ALCAP” type unit. In all cases, it is essential that they are fully operational, set to the optimum temperature and the throughput
set to an appropriate flow rate.

Treat your fuel right and you will have fewer problems.