TM 5-5420-203-14
2-2. GENERAL - CONT
c. Classifications and Definitions of Leaks for Operator/Crew PMCS:
CLASS I: Seepage of fluid (as indicated by wetness or discoloration) not great enough to
form drops.
CLASS II: Leakage of fluid great enough to form drops but not enough to cause drops to
drip from item being checked or inspected.
Equipment operation is allowable with minor leakage (Class I or II). Consider
the fluid capacity in the system being checked or inspected. When in doubt,
notify your supervisor.
When operating with a Class I or II leak, continue to check fluid levels as required
in your PMCS.
CLASS III: Leakage of fluid great enough to form drops that fall from the item being
checked or inspected.
Class III leaks shall be reported to your supervisor or organizational maintenance
d. Classifications and Definitions of Stage I, II, III, and IV Corrosion.
STAGE I CORROSION: Discoloration or staining. This stage of corrosion appears as a
thinly gray, black, or reddish film on ferrous metals; as a white or gray film on aluminum,
magnesium, zinc, and their alloys; and in varied colors (green, blue-green, brown, or black) on
copper and copper alloys. This is the initial stage of corrosion; it does not extend beyond the
surface of the metal and is easily removable.
STAGE II CORROSION: Etching. When rust or corrosion is removed, the surface of the
metal is roughened, but no holes in the surface are distinguishable.
STAGE III CORROSION: Pitting. With this type of corrosion, holes in the surface of the
metal are visible to the naked eye after corrosive coating is removed from the metal.
Material showing signs of Stage III Corrosion is generally unacceptable, but may be
upgraded to Stage II or fully repaired using approved procedures for repair of corroded
material. Refer to MIL-C-11080, Corrosion Resistant Coating.
STAGE IV CORROSION: Scales, pitting, and powdering. Corrosion in this stage has
progressed to the point where fit, wear, function, or life of the part has been affected.
Powdery or scaly conditions accompanied by deep pitting and/or irregular flaking of metal is
encountered in this stage of corrosion.
Material containing Stage IV Corrosion is generally unacceptable, except in the case of
castings or heavy plate. This material is acceptable after corrosion removal and repair if
the function is not affected and surface roughness requirements are met.
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