FED-STD-791D
Method 3411.1
September 30, 1986
THERMAL STABILITY AND CORROSIVITY OF
AIRCRAFT TURBINE ENGINE LUBRICANTS
1. SCOPE
1.1 This method describes a procedure for determining the thermal stability and
corrosiveness of aircraft turbine lubricants in an environment free of air and moisture. The
catalytic effects of mild steel on the decomposition of the fluids and the corrosion of the steel by
the thermal degradation products of the lubricant are measured.
2. SUMMARY
2.1 A weighed mild steel specimen is placed in a glass thermal stability test cell with a
measured amount of test lubricant. Air and moisture are removed from the test cell by heating
and shaking under vacuum prior to sealing the tube. The sealed test cell is then heated at a given
temperature for a specified period of time. The stability of the lubricant is assessed by
determining the change in viscosity, total acid number and by the appearance of the residual
lubricant at the end of the heating period. The steel specimen is weighed and examined under a
microscope to determine changes due to corrosion.
3. SAMPLE SIZE
3.1 Approximately 10 mL for each steel corrosion test.
4. REFERENCES, STANDARDS, AND APPARATUS
4.1 Test cell A borosilicate glass test cell having the dimensions given in Figure l is
recommended as the sample container.
4.2 Heating bath, 9.5-L (10-qt) capacity, (manufactured by Sta-Warm Electric, Ravena,
Ohio or equivalent). An aluminum block may be used in place of the heating bath if so desired.
The resistance wire-heated aluminum block must have a suitable number of openings of the
proper diameter (approximately 2.0 cm) and depth (approximately 21 cm) so that the sealed test
cell is completely immersed in the heater. The temperature of the aluminum block or heating
bath shall be capable of being controlled within 1°C ( 2°F) at the test temperature. The
temperature gradient between oil sample and the aluminum block or bath shall be kept within
1°C (2°F).
4.3 Test cell holder When a heating bath is used, a heavy-wall steel sample tube holder
of the proper size to contain the test cell shall be provided for safety reason.
4.4 Becton, Dickinson and Company Yale Luer-Lock (20YL), or equal 20 mL
hypodermic syringe with a No. 14 square-tip needle approximately 20 cm (8 in) long.
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