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Change-over to low sulphur fuel – a practical example to consider

From feedback recently received from one of our surveyors, we give an example of a change-over from high sulphur to low sulphur fuel operation that did not work as intended.

More stringent requirements for low sulphur fuel (LSF) operation came into force on 1 January 2010 (EU ports) and the requirements concerning operation in European and Californian waters will stepwise become stricter.

The Revised MARPOL Annex VI including maximum sulphur limit requirements (1.00% by mass) for Emission Control Area entered into force on 1 July 2010.
The amending directive 2005/33/EC, which requires a max sulphur content of fuel in use of 0.1% at berth in EU ports, entered into force on 1 January 2010. We may therefore expect an increased focus on sulphur content of fuel in use, from Port State Control (PSC) officers and harbour authorities in EU, during this autumn and onwards.

The situation described by the surveyor was the following:
During surveys by DNV for the issuance of statements in connection with change-over from MGO to low sulphur MGO while entering/operating in EU/CARBS areas, it was found that when the actual fuel in use was tested, the sulphur content exceeded the statutory maximum sulphur limit, even though the Master and officers in charge were under the impression that the
fuel change-over had been completed satisfactorily.

In discussions with the client, their preliminary investigation revealed the following:
1. The sulphur content of the previous oil in use was 1.00%.
2. The vessel was trading in a SOx Emission Control Area at the time.
3. There was previous contamination in MGO (Marine Gas Oil) tanks and tanks were not cleaned prior to bunkering LSMGO.
4. The fuel was mixed in the tank (with probably too large a volume of mixing) and there had been poor flushing of lines prior to starting mixing.

5. The change-over was based on a pure volume exchange and no mixing volume based on the consumption rate/sulphur content differential had been considered. They believe it is difficult to estimate the volume of deposits on the piping walls and how fast this coating releases sulphur.

6. Some of the fuel was actually slightly off specification. This was discovered after testing by DNV Petroleum Services (DNVPS).

Possible explanation
When dealing with change-over procedures, it is imperative to realise that many fuel supply systems are closed-loop systems
in which the fuel is continuously circulated.

When changing over from HFO (Heavy Fuel Oil) service tanks to LSF service tanks, there will be no immediate change of supply
to the consumers (engines, boilers), only a dilution of the fuel circulating in the supply system
 
For more info please download original DNV technical bulletin

 

For more information, please contact:
DNV Classification Support
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Machinery and Systems

 

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