Lessons learned: Presence of waxy crystals in fuel can block fuel filters


Incident 

After delivering a high-latitude cruise experience for its 670 passengers, a cruise ship was heading south again.

When navigating in Arctic waters, the cruise ship had been running on heated low sulphur fuel.

Once close to home, the fuel supply to the main engines and electrical generators was changed over to marine gas oil (MGO), in preparation for entering harbour.

Soon after the fuel supply changeover, a total electrical failure was experienced.

All power and propulsion was lost, but the emergency generator started automatically to maintain essential services. The cruise ship was then drifting and not under command.

Realising there had been an issue with the fuel, the ship’s engineering team restored power and propulsion by changing over to an alternative heavy fuel oil (HFO) supply.

Generator power was restored within 5 minutes and, about 10 minutes later, propulsion was available again and the cruise ship entered harbour without further incident.

Credit: UK Maib Safety Digest

Lessons learned:

  • Post-incident analysis established that, immediately after the changeover to MGO, the fuel filters were blocked due to the presence of waxy crystals in the fuel (Figure 1). MGO reacts to temperature changes, with a key efect being the formation of crystalline wax particles as the temperature falls.
  • In this case, the ship had been operating in Arctic waters where the air temperature had dropped to minus 14°C and the sea temperature was between 3°C and 5°C. In these conditions, the ship’s engine room ventilation system allowed the ambient temperature to drop to very low levels, resulting in signifcant cooling of the MGO pipework.
  • This created the environment for the crystals to form in the MGO fuel lying dormant in the supply pipework, which blocked the flters soon after the MGO fuel supply was selected.
  • A number of actions could have been in place to minimise this risk, specifcally: pipework insulation, pipework heating, circulation of the fuel back to the service tanks or the use of a fuel additive.

As Safety Digest concluded:

The ship’s engineering team reacted effectively to the situation, identifying the problem and restoring the fuel supply. Their system knowledge and practised procedures for changing fuel supplies allowed the situation to be recovered rapidly with power and propulsion restored in a timely manner.



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