FED-STD-791D
Method 202.1
September 30, 1986
CLOUD INTENSITY AT LOW TEMPERATURE
1. SCOPE.
1.1 This method is used for determining the stability (at low temperature) of hydraulic
fluids or highly refined light lubricating oils.
2. SUMMARY
2.1 The method consists of storing a sample at -54C (-65F) or lower for a period
required by the petroleum product specification, agitating it, and comparing its turbidity with a
standard. The sample is poured in a sealed, cleaned, dried sample bottle and stored for a
specified number of hours at a maximum of -54C (-65F). Within 5 min of the comparison
time, the turbidity standard is shaken vigorously for 10 s and poured into a sample bottle. At the
end of the storage time, the sample is removed from cold storage and shaken vigorously for 10 s.
The frost is eliminated from the sample bottle and it is compared with the turbidity standard.
The turbidity of the sample relative to the standard is reported as less than, more than, or equal to
the standard.
3. SAMPLE SIZE.
3.1 Approximately 120 mL of test oil (or fluid).
4. REFERENCES, STANDARDS, AND APPARATUS.
4.1 Cooling apparatus, -54C (-65F) or lower (ASTM cloud and pour point apparatus,
or equal).
4.2 Sample bottles (2), clear-glass 120 mL, with cork stoppers.
5. MATERIALS.
5.1 CAUTION - SOME MATERIALS ARE TOXIC AND HAZARDOUS. The
chemical materials listed in this section must be handled carefully. Federal Test Method 10000,
Material Handling Safety Precautions, is a reference which lists all toxic and hazardous materials
cited in FTMS 791. The synonyms, life hazard, flammability, handling and storage precautions,
emergency treatment and measures, and spill practices of each chemical are explained.
5.2 Methanol-glycerol (technical grade), 1:1 solution (by volume) [1,3,0].
5.3 Turbidity standard, prepared within 30 min of use, as follows:
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