CORROSION PREVENTION AND CONTROL (CPC) - Continued
SELECTIVE LEACHING: One element, usually the anodic element of an alloy, corrodes away, leaving the
cathodic element. This can create holes in metal.
INTERGRANULAR: Metal deterioration caused by corrosion on the bonds between or across the grain
boundaries of the metal. The metal will appear to be peeling off in sheets, flaking, or being pushed apart by
layers. A particular type of intergranular corrosion is exfoliation.
PITTING: This can result from conditions similar to those for crevice corrosion. Pits can develop on various
materials due to their composition. Rifle boxes are big victims of pitting.
EROSION: Results when a moving fluid (liquid or gas) flows across a metal surface, particularly when solid
particles are present in the fluid. Corrosion actually occurs on the surface of the metal, but the moving fluid
washes away the corrosion and exposes a new metal surface, which also corrodes.
FRETTING: Occurs as a result of small, repetitive movements (e.g., vibration) between two surfaces in contact
with each other. It's usually identified by a black powder corrosion product or pits on the surface.
GALVANIC: Occurs when two different types of metal come in contact with each other, like steel bolts on
aluminum, for example. This is a common problem on aircraft because of their mix of metals.
STRESS: Term used to describe corrosion cracking and corrosion fatigue. Where an item is not ready/available
due to one of these forms of corrosion, it shall be recorded as a corrosion failure in the inspection record and the
appropriate code (170) for corrosion shall be used when requesting/performing maintenance.
SF Form 368 should be submitted to the address specified in DA PAM 750-8.
Equipment operation is allowable with minor leakages (Class I or II) except for fuel leaks.
Of course, consideration must be given to the fluid capacity of the item or system being
checked. When in doubt, ask your supervisor. Failure to comply may result in damage
When operating with Class I or II leaks, continue to check fluid levels as required in your
PMCS. Class III leaks should be reported immediately to your supervisor.
It is necessary for you to know how fluid leakage affects the status of the engine. Following are types/classes of
leakage you need to know to be able to determine the status of the engines. Learn these leakage definitions and
remember - when in doubt, notify your supervisor.
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
Class III - Leakage of fluid great enough to form drops that fall from item being checked/inspected.
END OF WORK PACKAGE