Bunker flash: High concentrations of catalytic fines, elevated acid numbers found in Singapore

Bunker fuel testing and marine surveying business Maritec-Naias on Friday (12 June) issued an alert regarding high levels of catalytic fines and elevated acid numbers present in multiple VLSFO bunker samples from deliveries in the Singapore port: 

During the period of 20 May 2026 and 02 June 2026, Maritec Pte. Ltd. (hereafter referred to as Maritec-Naias) conducted testing on five samples representing Very Low Sulphur Fuel Oil (VLSFO) deliveries from two suppliers in the Singapore port. The analyses revealed Aluminium and Silicon (Al+Si) concentrations ranging from 61 mg/kg to 68 mg/kg.

It is important to note; these values exceed the ISO 8217:2010/2017 specification limit of 60 ppm but remain within the permissible tolerance limit of 72 ppm under ISO 4259 for a single test result. In this regard, Catalytic Fines content, (Aluminium+Silicon), above 60 ppm is regarded as high. Of the five samples, three originated from one supplier, while the remaining two were from another.

Aluminium and Silicon constitute the principal classes of abrasive solids in fuels. Elevated concentrations of such particles at the engine inlet can precipitate abnormal wear and tear of fuel system components, piston rings, and cylinder liners. To safeguard against this, many engine manufacturers stipulate a maximum threshold of 15 mg/kg Al+Si at the engine inlet.

The primary method of mitigating Catfines is through an efficiently operating fuel purification system. Monitoring Aluminium and Silicon levels both before and after centrifugation provides a reliable measure of the system’s effectiveness in removing these contaminants.

During a similar period, Maritec-Naias also tested fifteen bunker fuel samples representing VLSFO that exhibited elevated Acid Numbers, ranging from 2.0 mg KOH/g to 2.5 mg KOH/g. While these values remain within specification limits, they are nonetheless considered at higher side. Elevated Acid Numbers may stem from contamination with acidic compounds such as Phenolic compounds and Alkyl Resorcinols, often associated with Estonian Shale Oil. Such contaminants can lead to operational complications including sludge formation, fuel pump seizures, and compromised injection equipment cleanliness.

Maritec-Naias Recommendations

• High Catfines monitoring: Maritec-Naias advises collecting samples at critical points within the fuel system — including the fuel oil tank transfer pump, before and after centrifuge, service tank, and after fine-filter — to evaluate the efficiency of fuel cleaning.
• Elevated Acid Numbers: For fuels with elevated Acid Numbers, Maritec-Naias recommends conducting Gas Chromatography-Mass Spectrometry (GC-MS) using the Solid Phase Extraction (SPE) method to identify the specific acidic compounds present or upgrading your marine fuel testing package to MFTP Plus, which enables pre-emptive monitoring to detect major harmful substances prevalent in the market, such as Cashew Nut Shell Liquid (CNSL), Phenolic compounds and Alkyl Resorcinols that cause damage to equipment.

Maritec-Naias states, while all data and findings presented in this document are true, it does not reflect on the overall quality of fuel being supplied in Singapore region. If you intend to bunker at this region, please request for a Certificate of Quality (CoQ) prior to loading.

Photo credit: Hans Reniers on Unsplash
Published: 15 June, 2026