VPS: Abrasive Catfines Can Damage Marine Engines
A common concern of maritime chief engineers, regarding vessel engine damages, is the presence of highly abrasive “catfines” within marine fuel. To fully understand the seriousness of this issue, we first need to understand the source of the problem.
Oil refineries use catalysts in their Fluid Catalytic Cracking Units (FCCU) or “Cat Plants” to process crude oils in the production of numerous products from the source crude. These catalysts are high in aluminum silicate (Al+Si) content and over time and repeated use, can breakdown and fragment into smaller particles, or catalytic fines. These catalytic fines, known throughout the industry as “Catfines” can eventually find their way into the heavier refining streams and consequently the HSFO and VLSFO fuels being burnt onboard vessels. Higher levels of catfines within the fuel can be extremely abrasive and damaging to ships engines.
It is critical to note the ISO8217 specification limit for Al+Si for residual fuels delivered to the ship, is 60 mg/Kg for all revisions post-2005. This level is significantly greater than the OEM engine inlet limit of 15mg/Kg and therefore the fuel requires efficient onboard purification, monitored via a frequent fuel-system-check, process in order to avoid potentially catastrophic engine damages.
From a recent review of more than 3,000 Fuel System Check samples taken before-purifier and after-purifier, VPS found 16% of the fuels after-purifier catfine concentrations were above the 15mg/Kg OEM limit. This indicates that some 480 vessels had purifiers failing to operate to their optimum efficiency in order to protect the engine.
At this time of the Middle East military conflict, one might suspect that refinery output around the wider region to have been impacted by crude availability, thus reducing the ultimate throughput of any refinery. However, under certain refinery operating conditions, reduced throughput may lead to higher relative concentrations of catfines in heavier streams. Thus these catfines can potentially end up in marine fuel supply chains.
In 2-stroke crosshead engines, ineffective removal of catfines can result in their entry into the combustion chamber, where they cause abrasive wear between piston rings and cylinder liners. Conversely, medium speed engines tend to be generally more tolerant, due to continuous oil circulation and filtration, but still vulnerable if catfine levels are excessive.
Another consideration within this equation is that cylinder oil (used exclusively in 2 stroke engines) is “single use” and exhausted after first use. Thus it’s overuse, in any attempt to combat catfines and minimize wear can be commercially punitive, unnecessary and in some cases contribute to damages, exacerbating the “grinding paste” effect occurring within the cylinder liners.
Cylinder lubricants are primarily a base oil, plus an additive “pack” (a combination of carefully selected compounds focused on providing various qualities e.g. Base Number (BN) to combat fuel sulphur and detergency to clean etc). However, inappropriate cylinder oil selection, or excessive feed rates may contribute to deposit formation on piston crowns and ring zones.
Over-lubrication is not an effective mitigation strategy as it may increase deposit formation and will certainly increase operating costs.
A first step to prevention of catfine damage would be in the selection of a reputable supplier, known for delivering low-catfine fuel. Data in relation to this is highlighted in the VPS PortStats application. However, its recognized on numerous occasions, the owner/operator of the ship dealing with sub-standard fuel is not the entity who purchased the fuel. Therefore, further practical considerations should also be made including, appropriate tank cleaning, circulation and movement to avoid catfine settling and concentration at much higher levels than the original test results obtained from the vessel manifold sample.
In the case of managing catfine levels above OEM engine entry limits, effective purification remains key. Statistically, a vessel will suffer one to two instances of main engine damage over the course of her operational lifetime. These costs can reach millions of dollars, far more than the average main engine damage costs of $650K highlighted in the Swedish Club paper “Engine Damage."
Monitoring and Quality Control – Fuel System Checks (FSC)
It is essential that fuel samples are taken both before and after purifier. This should be carried out at regular intervals (on a quarterly basis), with increased frequency when high catfine levels are identified. In addition, whenever VPS see a vessel manifold sample with a catfine level >40kg/Kg, an alert is automatically sent to the vessel, with the instruction to take additional before and after purifier samples, as a cautionary procedure.
There are numerous reasons why regular fuel system checks are critical:
• Help identify potential risks & operational issues before major damage occurs.
• Confirm that the system’s flow rate, temperatures, discharge cycles are properly adjusted to handle the specific fuel that is being treated
• Verify that the fuel treatment system is properly maintained
• Reduce operating cost and increase lifecycles of critical components
• Identify presence of unusual components that can enter fuel post- delivery.
Periodic sampling from the fuel treatment system will also identify problems such as water ingress from ballast systems, leaking heating coils and cargo contamination.
Core Operating Conditions
In addition to the FSC program it is key to undertake the following practices:
Maintain the correct inlet temperatures as purifiers rely on centrifugal separation, enhanced by density differences. The fuel must be heated to the manufacturer-specified temperature for optimal separation and reduced carry-over.
Ensure the separator is correctly configured and operated (e.g. gravity disc selection in conventional units or proper control settings in automated systems) to avoid reduced separation efficiency, which could allow water or catfines to pass through to the engine.
Keep the feed-rate of fuel slow and steady. Running purifiers in parallel at minimum feed-rate improves separation and reduces carryover.
Match settings to oil density. Density changes with fuel grade, so adjusting settings ensures proper bowl separation.
Maintenance Practices that Directly Improve Efficiency
Clean filters and heaters regularly. Blocked filters or fouled heaters reduce flow and temperature stability, lowering purification quality.
Clean fuel tanks at scheduled intervals. This prevents high sediment and catfine concentrations from overwhelming the purifier.
Avoid by-passing any fuel-treatment equipment. By-passing risks engine damage and eliminates the purifier’s protective function.
Ensure adequate spare parts are onboard. Worn seals, gaskets, or disc stacks, reduce bowl pressure and separation efficiency.
Follow the vessel’s preventative maintenance schedule and manufacturer’s intervals. Planned maintenance ensures consistent cleaning, inspection and overhaul cycles.
Summary
So, with the recent survey by VPS finding 16% of fuels after-purifier catfine concentrations were above 15ppm, this highlights the fact, these purifiers are failing to operate to their optimum efficiency and their primary function to protect the engine.
All the above, monitoring, quality control and operational steps, are key to ensure a vessel’s engine is protected from the abrasive wear catfines can cause. Plus, by following this advice, the vessel will see an improvement in combustion efficiency due to burning cleaner fuel. This will all result in reduced downtime and repair costs, avoiding purifier failures which can lead to major engine issues.
