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Veritas Petroleum Services (VPS) has issued a bunker alert for Fujairah relating to high sodium fuels. It is the second warning issued by VPS this year for the Middle East's biggest bunker port.

So far in 2018 there have been seven VPS high sodium fuel alerts - the other six being for Cartagena, Haifa, Limassol (2), Singapore and Zeebrugge.

According to the latest ISO 8217:2017 standard for marine residual fuels, the maximum sodium limit is 100.0 mg/kg for RMG and RMK grades (RMG 180, RMG 380, RMK 380, RMG 500, RMK 500, RMG 700 and RMK 700) and also for RMB 30 and RMD 80, whilst for RMA 10 and RME 180 the limit is 50.0 mg/kg.

The International Bunker Industry Association (IBIA) notes in its document 'Vanadium and sodium in marine fuels' that the form in which the sodium is present determines the extent of the possible reduction in the ship's fuel treatment plant.

Sodium associated with water contamination can usually be effectively removed by a well-operated centrifuge system, whilst sodium contamination in the absence of water is probably the most difficult form of this contamination to remove.

High-temperature corrosion and fouling can be mainly attributed to both the sodium and vanadium content of the oil. Both elements oxidise during combustion and, in a series of chemical reactions, form semi-liquid and sticky low-melting-point salts that adhere to exhaust valves and turbochargers. These salts are corrosive and attack the metal to which they adhere.

It is in combination that sodium sulphate and vanadium pentoxide can be harmful to the operation of the engine. They are responsible for fouling and high temperature corrosion on the exhaust valves; also, high sodium levels can result in increased ash deposits in the exhaust gas system and turbochargers.

Last year, there were six VPS alerts related to sodium in residual fuels, with two warnings each for the Americas, Europe and Middle East. It was the fourth most common residual fuel issue to be flagged up in 2017 - after density, cat fines and sediment.