MIL-DTL-5521C
4.6.14 Corrosion and adhesion test. Ten MS35803-214 hydraulic packing back-up washers or leather
specimens of approximately equivalent size shall be prepared for corrosion testing by inserting
specimens in a desiccator or similar humidity chamber maintained at 95 percent minimum relative
humidity and at room temperature for 72 hours minimum. Metallic plates of the metals listed below shall
be polished to a surface roughness of 8 to 16 microinches root mean square (rms) finish. The edges
shall also be polished to reduce the formation of edge corrosion. Plates shall be washed with
precipitation naphtha as specified in FED-STD-791 or similar degreasing agent. The metals used shall
be as follows:
a. Aluminum-alloy (AMS-QQ-A-250/4)
b. Brass (ASTM-B36/B36M)
c. Bronze (ASTM-B139/B139M)
d. Steel (AMS 6350)
e. Stainless steel (AMS-S-7720, Condition A)
The humidified back-up washers and the metallic plates shall be immersed in MIL-PRF-6083 rust
preventative fluid (MIL-PRF-5606 fluid base), and drained to the drip point. The washer and plates shall
then be laid together in a stack so that at least two back-up washers contact each specified metal. The
stack shall be held together with a pressure of 20 to 30 pounds and placed in a desiccator which is held
at 90 to 95 percent relative humidity at room temperature. A separate set of metallic plates shall also be
prepared (buffing, cleaning and dipping in the same rust preventative fluid and drained) and placed in the
desiccator in such a manner that the control plates do not touch each other or any of the back-up
washers. ((Di-potassium acid phosphate when placed in distilled water in sufficient quantity to produce a
saturated solution, will maintain approximately 92 percent humidity in a sealed desiccator at 20° C (68°F)
temperature.)) Time of immersion for this portion of test shall be 96 hours minimum for all inspection
tests and 14 days minimum for all qualification test analyses. No more than 15 minutes should elapse
between the time the test samples are removed from the pre-humidifying chamber and placed in the
stacked condition in the second humidity chamber. At the termination of this test, there shall be no
adhesion of the leather to the metals nor shall there be any evidence of pitting, erosion, corrosion or bad
discoloration, as determined by the following procedure: Inspect the surfaces of the plates which were in
contact with the back-up washers for discoloration, deposits, pitting et cetera. If any exist, the surfaces of
the plates shall be washed in precipitation naphtha. Deposits determined as leather which can be
removed by this process and which do no occur on the separate control plates shall be construed as
adhesion. If any other marks remain on the surfaces of the plates after inspection, the surfaces shall be
lightly polished with a nonabrasive cloth buff. Any pits or eroded marks remaining after this process shall
be construed to be corrosion. Discoloration or staining (marks which do not physically affect the surfaces
of the plates and which easily wash or buff off) shall not be considered detrimental.
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