Incident:
Two out of six units suffered high exhaust gas temperatures while a Bulk Carrier was at Sea. After investigation, it was found that several piston rings were broken in both the units. The ship staff replaced the piston rings with spare ones. The vessel resumed voyage hoping to reach port as there were no more spare piston rings. Unfortunately, the main engine abruptly stopped at sea and the engineers found more piston rings broken from various other units. The engine did not start on fuel, where the vessel was towed to the nearest port.
After all investigations, the engineers suspected the fuel to be the cause. But, to their surprise, the fuel quality test reports revealed that there was no fault in its quality.
Investigations:
- The Bulk Carrier had Double-bottom fuel oil tanks where the air vent pipes passed through the cargo hold.
- These air vent pipes were found to be severely damaged and at certain places, it was even found holed.
- The Cargo holds had the most number of damaged air vent pipes and damaged parts were found close to the transverse bulkhead structure.
- An analysis confirmed that fuel oil samples contained a high percentage of Alumina (Al2O3). The ship confirmed that it had alumina as one of its cargo earlier.
Thus, the extent of damage was so high that:
- All fuel injectors were replaced
- All fuel pump elements renewed
- All Liners were out of maximum allowable wear limits
- Piston rings were replaced and some of the crowns had worn grooves
- Every damaged air vent pipe was replaced with new pipe section
The abrasive cargoes entering the fuel oil system through holed or wasted pipelines was the cause for the damages as mentioned above. Fuel oil separators can remove only specific quantities of this type of substance but not massive quantities. It is to be noted that the purifiers cannot remove water efficiently if water is above 3% and thus associated contaminants.
Similarly, in one other case, an investigation into the main engine revealed that certain parts were heavily worn because of the presence of aluminium particles in fuel. Samples taken from the main engine fuel oil inlet line showed contamination in the order of 200 ppm, while oil samples taken from the service tanks (drain) contained up to 2,000 ppm, whereas the engine manufacturers’ upper limit was 15 ppm.
How to avoid such situation:
- Vessel pipe should be designed in such a way that it is placed at sufficient distance to other structure to provide easy inspection of the whole circumference of the pipe.
- Due attention should be paid by the vessel owners and surveyors in examining the air pipes in detail, in particular where it is located close to other structures like ship side, bulkheads, etc. during the operation of the vessel.
Lessons Learnt:
- Frequent inspection of sounding and air vent pipes of fuel oil tanks are highly essential.
- During a cargo hold survey, a special attention on fuel oil tanks transfer lines, sounding and vent pipes are essential and has a potential risk of cargo contamination.
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Source: Officer of the Watch
