Marine fuel compatibility

Compatibility challenges have always been present when mixing heavy fuel oils (HFO), and the growth of environmental legislation has made it even more important to be aware of fuel compatibility issues.

Switching to and from Emission Control Area (ECA)-compliant fuels when entering or leaving an ECA poses a range of issues for vessel operators. Dissimilar fuels are being mixed more often, increasing the risk of compatibility issues like the formation of sludge, clogged purifiers, blocked filters and even power failure.

Best practices

Whenever possible, avoid mixing fuels of different types or from different sources.

Additional precautionary measures you can take include:

• Store fuels separately until compatibility testing has been carried out
• Test the products for compatibility in a reputable lab
• Avoid mixing fuels with greatly dissimilar densities

Onboard spot tests

In practice, it is often not possible to completely avoid any comingling. In those cases, it is best to limit the mix ratio to less than 20 percent.

In those cases, you should test a sample mix. An onboard spot test (ASTM D4740) can offer an indication of compatibility – although a more thorough laboratory-based test regime is advised.

It’s also important to note that spot tests do not work for comingled distillate products such as ExxonMobil Premium HDME 50 fuel.