Viswa Lab has witnessed numerous Piston ring breakage and Liner wear cases this year. Based on the statistics, it was reported that the main cause of such damages was closely related to high Cat-fines and water in the fuel.
A Recent Case:
A Containership was trading between China and Russia. The Vessel’s endurance is such that it required 1200 MT of bunker fuel to complete a round trip. As a routine, the bunker sample was analyzed at Viswa Lab before using the fuel.
Sequence Of Events:
- The Vessel changed over consumption from new bunkers.
- Within couple of hours of change over to new bunkers, the vessel experienced fine filter clogging.
- Associated with frequently clogged fine filters, there was drop in fuel pressure for the main engine.
- The vessel continued to use the fuel, by cleaning the clogged filters.
- At the next port, the Chief Engineer decided to inspect the Liner and Piston rings through the scavenge ports.
- 4 out of 6 units had severe piston ring breakage and pieces of piston ring was found in the under piston space (diaphragm plate) near stuffing box.
The Superintendent was informed about the problems being faced. In order to identify the root cause of the problem, engine maker’s inspection and overhaul of machinery was arranged. The Engine maker’s technical representative inspected all the parts and concluded the below.
- All the piston rings suffered a serious damage, and most of them were broken to pieces and had to be replaced.
- 2 Liners had to be replaced due to severe wear and scoring marks.
- Piston rod of one particular unit faced severe damage and scored.
The Ship owner/Manager requested Viswa Lab to test the fuel oil samples in order to mitigate the problems. It is to be noted that Viswa Lab has already carried out the regular full spec analysis as per ISO 8217:2005 and reported that fuel was off spec for
- Viscosity and
The Density of the fuel was 994.5 Kg/m3. Certain additional tests were performed on the fuel sample and below listed are the findings as revealed by Viswa Lab.
- Cat-fines was high (though within limits of ISO 8217 specifications) at 32 ppm. It is to be noted that the Engine Makers recommend to maintain cat-fines less than 15 ppm at the engine inlet.
- PFIN (Problem Fuel Identification Number) was higher than normal. Viswa Lab’s benchmark, PFIN (Problem Fuel Identification Number) addresses the fuels that cause main engine piston ring breakage. This is a serious problem endangering the safety of the vessel when the renewal of piston rings has to be carried out while the ship drifts at sea. Fuels having high MCR(greater than 11.5%), high asphaltene (greater than 10.5%) and high CCAI (greater than 849) were found to cause main engine piston ring breakage.
The piston ring and liner damage was due to cumulative effects of
- High Density fuel,
- Improper purification and filtration,
- High cat-fines exceeding 15 ppm engine maker limit,
- PFIN – high (Viswa Lab’s Bench Mark for identification of fuels which carry a potential for piston ring breakage).
We thank Viswa Lab for all the details and technical information provided to us.
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It is necessary to analyse every batch of bunker, as the analysis cost is negligible compared to the repair cost and down time / off-hire cost. Whenever high cat-fine is alerted, it is a good practice to drain settling tank and service tanks extensively when the first transfer from storage tank is done. The initial location for the bulk of heavier cat-fines to be settled down is in storage tanks. The first transfer from storage tank will carry most of these abrasive solids and deposit at settling tank bottom. If the bulk of cat-fine is removed by draining out from settling tank -even by wasting some fuel- severe damage could be avoided. Run both separators at lowest through put for best purification. Ensure hot filter is used. Increased frequency of back wash filter is an early warning that excessive cat-fine still exists in the processed fuel. Never by-pass back wash filter or reuse the bulk of drained out fuel from back wash drain tank. If the well processed fuel is not sufficient to maintain speed, consider to sail at reduced speed to match with the rate of fully processed fuel. That could be the best solution for overall performance for all parties