Engine Worn Out by Catalytic Fines

DNV has over the last years seen an increase in engine damage due to catalytic fines, even though the bunkered fuel has been in accordance with ISO 8217 marine fuel specification and fuel treatment is standard procedure and implemented for all vessels. Damage (incident occurred in 2010), that can be traced back to catalytic fines occurred after only 100 running hours, making the engine totally inoperable. All pistons and liners were totally destroyed and had to be changed.

With the new requirements related to the use of low sulphur fuel in certain areas and the fact that low sulphur fuels have a higher average amount of catalytic fines, it is expected to see more of this kind of damage; and care should therefore be taken to ensure that the fuel treatment and tank cleaning is operating satisfactorily at all times.

Immediately after a voyage in rough sea, the crew received a high temperature alarm on one cylinder unit on the main engine. When dismantled, the cylinder unit was found completely worn down and had to be exchanged during the voyage. When the vessel arrived in port less than 100 hours after the incident, the crew performed an inspection of all cylinder units. All units, including the newly exchanged one, were found worn to an extent where total overhaul and replacement were required.

Abrasive wear of piston ring.

Left. Abrasive wear of cylinder rings (looking through a scavenge air port from the outside).
Right. Abrasive wear inside the cylinder liner above the scavenge air ports.

Left. Micrograph (200x magnification) of a normal liner surface with open graphite structure. Dark areas are showing the graphite lamellae.
Right. Cylinder liner after less than 100 operating hours. Catalytic fines (shown by arrows), abrasive wear traces and closed/partly-closed graphite structure (some of them are encircled in red ovals). Blue arrows shows newly embedded catalytic fines.

Even though the fuel had been delivered within specifications, catalytic fines had over time settled in the fuel tanks. It was reported that the tanks were last cleaned 4 years prior the incident (typical cleaning interval is approximately every 5 years, normally at Main Class Renewal surveys). During the rough weather, the catalytic fines were rapidly circulated in quantities beyond the capacity of the fuel oil separators and the filters, and entered the engine, causing severe damage to the cylinder units. Below are the results from the HFO samples taken from the affected vessel during 2010:

Actual contents of catalytic fines (in ppm) from the HFO samples taken from the affected vessel during 2010. They are all well below 80 ppm, which is the maximum level for the fuel specification.

Catalytic fines are remnants of aluminium and silicone oxides used in the catalytic cracking process for converting crude oil into lighter petroleum products in refineries. The catalytic fines are meant to be recycled and will generally become smaller and harder for every cracking process they go through (they can be as hard as 7–8 on a scale where diamond is 10).

It is also important to note that low sulphur heavy fuel oil (LSFO) normally contains more catalytic fines than (ordinary) high sulphur heavy fuel oil (HSFO), which may be due to higher content of heavy cycle oils. Heavy cycle oils may in some cases have low sulphur content, while the content of catalytic fines can be very high.

Catalytic fines in ppm in low sulphur fuels, S<1% (blue), compared with regular HFO (red), samples from autumn 2010 (results from DNV Petroleum Services).

Engine makers generally recommend that the inorganic particles of size less than 5μm in the fuel should be less than 20 mg/kg (ppm) and that the contents of catalytic fines should be less than 15 mg/kg (ppm). The smallest particles are in general the most difficult to remove in the separators.

This implies that the vessel’s fuel treatment systems (separators and filters) should be able to reduce the catalytic fines contents from 80 ppm (as maximum delivered in the fuel) to max 15 ppm as recommended by the manufacturer.

From the above incident the following should be considered as lessons learned:

• Catalytic fines are aluminium and silicon oxides, which are very hard abrasive particles, and normally a small amount is contained in the fuel oil used by merchant ships. High amounts of catalytic fines following the fuel oil into the engine may cause excessive wear of the components in the combustion chamber (piston grooves, piston rings, cylinder liners) and of the fuel injection equipment.
• The ship’s crew should ensure that the vessel’s HFO separators work efficiently to reduce the level of catalytic fines and other impurities. This implies e.g. to ensure the correct HFO inlet temperature. Sometimes system capabilities and wrong set points may result in an inlet temperature which is too low (see manufacturer’s guidance for correct inlet temperature). A too low temperature will reduce the efficiency of the separation. It is also important to ensure an appropriate (low) feed rate to ensure purifying and not just pumping.
• Present experience from DNV Petroleum Services shows that in average low sulphur fuels contains higher levels of catalytic fines. However, most of the deliveries are still under the maximum 80 ppm required for the fuel oil specification (ISO 8217).
• Even with bunkered fuel with lower catalytic fines values than the limit, severe damage can occur from accumulated deposits in the storage, service and settling tanks. The ship’s crew should be extra vigilant in rough seas to ensure sufficient purification of the oil going into the main engine. It is advisable to run all available separators in rough weather if deposits of catalytic fines can be suspected in the tanks.
• More frequent cleaning of fuel tanks should be considered. These tanks should be drained and cleaned, maybe annually or more frequent if catalytic fines content of bunkers delivered are near to the maximum ISO specification figure for catalytic fines. Relying on Class survey intervals of opening up fuel oil settling and service tanks (cleaned for the purpose of structural inspection) may be inadequate.
• The ship’s management may consider taking Fuel System Check (FSC) samples of the fuel oil before and after each separator at regular intervals (maybe 4–6 months) to verify the efficiency of the separators. The samples should be sent to an established fuel analysing institute for analysis.

Source: DNV