IP 422: Determination of the filter flow of aviation turbine fuels at low temperatures (FFLT) (simulated freezing point)

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  • Method adopted/last revised: 1996
  • Method reapproved: 2011
  • REF/ISBN: IP422-2934869
  • Status: Current
  • First printed in STM books: January 1996


This standard specifies a method for determining the simulated freezing point, using automatic apparatus, of aviation turbine fuels, which may contain separated solids as wax.

The procedure can also be used to investigate the formation of wax crystals or the cold flow properties of other products, although precision has only been determined for aviation turbine fuels.

NOTE 1 The principle of this test relies on flow through a fine mesh test filter and hence the result can be affected by the viscosity of the sample.

When using procedure A, which employs a 26pm test filter, a no-flow condition is reached when crystals block the test filter or the viscosity exceeds approximately 14mm2/s; a sample with a viscosity of greater than 5 mm2/s at -20 °C can exceed the 14 mm2/s threshold at a temperature before crystals are formed. Where viscosity affects the result before crystals are formed, the reported value of the no-flow temperature of the sample will always be warmer than the actual freezing point, and therefore is fail-safe and an indicator of possible flow anomalies at low temperature.

NOTE 2 The results obtained using this standard have been found to be equivalent to those obtained using IP 16, except for liquids having a viscosity of more than 5mm2/s at -20 °C. which can give a higher temperature (warmer) result than IP16.

NOTE 3 The presence of contaminants that affect the size and growth of crystals can change the freezing point as determined by automated and automatic methods.

NOTE 4 The lowest temperature at which aviation turbine fuels remain free of solid hydrocarbon crystals, which may restrict the flow of fuel through filters in an aircraft fuel system, is a key safety parameter in the specification and use of fuels.

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