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17 September 2020


Dear Customer

As we move towards the cooler and wetter months of autumn and winter we once again wish to highlight the importance of taking a proactive approach to tank maintenance and water management.

The government’s Renewable Transport Fuel Obligation (RTFO) requires a percentage of petrol and diesel in the UK to come from renewable sources. This means the addition of ethanol in petrol and the addition of fatty acid methyl ester (FAME) in diesel. The presence of such renewable sources in petrol and diesel make water and tank management, throughout the supply chain, more important than ever.

In recognition of this challenge, we have further invested in our supply chain, ensuring only the highest quality of fuel is supplied to our customers, with the introduction of enhanced product filtration at our storage and distribution terminals.


In order to comply with the RTFO, diesel fuel in the UK now contains up to 7% of renewable bio diesel (FAME). FAME has certain characteristics which can result in complications if diesel storage tanks are not looked after correctly.

Complications relating to FAME:

1) FAME has solvent type properties which have a ‘cleaning effect’ on fuel tanks. This cleaning effect can remove dirt and result in clogged filters.

2) FAME also has ‘hygroscopic characteristics’ meaning it attracts and holds on to water. Water in diesel fuel can lead to the growth of microbes (Microbiological contamination).

What is microbiological contamination?

Microbiological contamination results from the growth of microorganisms, such as bacteria, fungi, and yeasts. Such microorganisms will grow wherever there is a source of water and fuel (as food).

Filters in pumps play an important role in protecting consumer’s engines from particles (dirt) in fuel. However, microbiological growth can result in the blockage of pump filters, impact the performance of the pumps (blocked filters will lead to slow delivery and nozzles out of action) and lead to increased corrosion.

IMPORTANT: As FAME helps to attract water into diesel fuel, it is now more important than ever to ensure that water is kept out of the storage system to reduce the risks outlined above.


As required under the RTFO the majority of unleaded petrol sold in the UK contains up to 5% ethanol.

Phase separation:

Contact between petrol containing ethanol and a sufficient volume of water due to water in the bottom of the storage tank can cause “phase separation” of the ethanol from the petrol. This will occur because the water is absorbed by the ethanol causing it to segregate from the petrol. The result is the formation of a water-ethanol layer in the bottom of the tank which leaves clean but octane deficient petrol above it.


As outlined above, water in the fuel storage system can cause significant problems for BOTH Diesel and Unleaded fuel. This is especially important in the cooler and wetter months of autumn and winter.

How can water get into the fuel storage system? Entry points for water include:

a) Free water can occur due to ingress or leaks as a result of, for example, heavy rainfall or through cracks in equipment

b) Water vapour (humid air) can enter storage tanks through air vents followed by cooling or condensation on tank walls

What can I do to help avoid issues associated with water in the fuel storage system?

• Routinely inspect the fuel storage system for areas of possible water intrusion:
o Verify that tank lids and fill caps are securely in place;
o Ensure gaskets are not cracked or worn;
o Check that spill buckets are clean and dry;
o Verify that the steel vent line riser is not corroded at the base where water could intrude; and
o Ensure that any surface drains near the underground tanks are clean and free of debris.

• All sites should be conducting daily checks to ensure that tanks remain free of water. Many sites will have an electronic tank gauge system that will detect the presence of water at the bottom of the tank. For sites without an electronic gauge, tanks can be dipped using a water-finding paste.

• Monitor dispenser flow rates for slow flow and if indicated, change the filters.

• Pump filters should be checked regularly to avoid the build-up of sludge content.

• Respond immediately to any customer complaints regarding the quality of the fuel.

• Consideration should be given to a pro-active tank cleaning regime.


United Fuels