Ask the expert: Water contamination

LaRese: LaRese: "If worrying levels are found, run two purifiers in parallel with minimum flow and keep the fuel inlet temperature at 98°C to ensure efficient purification"

Experts from ExxonMobil answer questions on cylinder lubrication and engine condition in our regular column. This time, technical liaison manager John LaRese discusses water contamination.

Q: I’ve been assured by my bunker supplier that the water content of the fuel I purchased is within spec. However, my vessel is suffering from the types of issues normally associated with high levels of water contamination. What could explain this and what should I do?

A: The presence of excessive water can be an unintentional consequence of external factors. It’s often the result of condensation, especially when operating in areas with a hot, humid climate such as Hong Kong and Singapore. Other sources could include steam leaking from heating coils or rainwater entering under tank lids.

Water contamination can enter the system during fuel transfer from the barge but may also be the result of human intervention in order to bulk out a bunker delivery with water. Whatever’s the case, you’re right to be careful. Even a 0.5% water level – which is the allowable upper limit of ISO 8217:2017 – amounts to 5 metric tonnes in a 1,000 metric tonne bunker delivery. If, for example, you are being charged $300 per metric tonne, this is the equivalent of $1,500 missing fuel. This does not include the potential cost of disposing of the 5 metric tonnes of water drained off the fuel.

Aside from the undesirable cost implications, the presence of water – especially above the ISO limit – can result in avoidable maintenance issues, which can trigger further unnecessary expenditure to rectify. The first step should therefore be to get a sample of your fuel tested by a reputable laboratory to determine the level of the water contamination. You’ll then be able to take suitable remedial steps to deal with the issue, such as ensuring settling tanks are at the right temperature and centrifuges are correctly set-up.

One of the most important steps is to ensure good housekeeping on board. For example, fuel tanks should be regularly drained of accumulated water and leaking steam heating coils should be repaired or taken out of service to eliminate additional water contamination. Other areas of water egress should be identified and rectified as well, such as fuel tank vents.

The range of water-related issues is wide, complex and interlinked. If an excess of water is present, the purifiers should always be checked to ensure that they are set up correctly and operating at the lowest possible throughput to suit the vessel’s consumption rate. If the effectiveness of your fuel treatment system is compromised then water could reach the engine where it could damage the injection equipment or impair the combustion process, leading to reduced vessel power. There is also the possibility of corrosion and the dilution of cylinder lubricants, which can lead to scuffing on liners and piston rings.

If the water is found to be sea water then there’s a much more severe problem due to the high salt levels, which can lead to corrosion-related issues. Sodium from sea water that dissolves in the fuel can combine with any vanadium present in the fuel during combustion, which triggers the production of low-melting point deposits that adhere to exhaust valves, seats and turbocharger turbine blades, leading to mechanical damage. This in turn can attract other combustion deposits, leading to mechanical damage. As with pure water, salt water can be removed on-board by draining all fuel tanks and proper operation of centrifuges/purifiers.

Given the potential scale of problems that water in fuel can create, it is essential for vessel operators to monitor and take action when water is present as even low levels of contamination can result in expensive and ultimately avoidable damage.

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