FED-STD-228A
3.1.8 Equipment for complete circulation of the heating medium.
3.1.9 A source of oxygen under pressure.
4. PROCEDURE
4.1 Unless otherwise specified in the detail specification, the test shall be carried out at a temperature of
70° ± 1°C (158° ± 2°F) and an oxygen pressure of 300 ± 10 pounds per square inch for a period of 94
hours ± ½ hour.
4.2 Unless otherwise specified in the detail specification, tensile strength and elongation tests, methods
3021 and 3031 respectively, shall be used to determine the deterioration of the insulation or sheath due
to aging.
4.3 After adjusting the aging chamber to the required temperature, the specimen shall be suspended
vertically in the chamber which shall be closed immediately and the oxygen pressure applied. At least 10
milliliters of capacity shall be available for each gram of oxidizable material. The exposure period shall
start at the time the specimen is placed in the chamber and shall continue for the required time under the
required conditions without opening the vessel.
4.4 At the end of the exposure period, the pressure in the aging chamber shall be released at a slow and
uniform rate, requiring at least 5 minutes for a complete release of the pressure. This procedure is
necessary to avoid possible formation of porosity in the specimen. The specimen shall be removed from
the aging chamber immediately after the release of the pressure and then set aside on a flat surface to
rest for not less than 16 hours and not more than 96 hours at room temperature before tests are made.
4.5 At the end of the rest period, unless otherwise specified in the detail specification, 4.2, tensile
strength and elongation shall be determined on the aged specimen as described in methods 3021 and
3031, respectively. If other properties are required, the specimen shall be tested as described in the
specified method. The same test shall be conducted on aged and unaged specimens for the purpose of
comparison in determining the degree of deterioration of the aged materials.
4.6 Adequate safety precautions shall be taken when heating oxidizable organic materials in oxygen
under pressure since the rate of reaction may become very rapid in some cases, particularly if a large
surface area is exposed and very high pressures may develop. Care shall be taken to avoid the
introduction of grease or oil into the chamber.
5. RESULTS
5.1 Calculation. The change in tensile strength, elongation, or other characteristic of the insulation or
sheath of the inspection unit due to aging, shall be calculated as follows:
Change in characteristic, percent=O-E x 100
O
where:
O=the value obtained on the unaged insulation or sheath of the inspection unit
E=the value obtained on the aged insulation or sheath of the inspection unit
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