Essay (cat A)
Topic - [Materials and Techniques for Aircraft Corrosion
Prevention ]
Methods for preventing aircraft corrosion
Reference AOPA [Aircraft owners and pilot association ]
Types of corrosion
Types of corrosion normally found on aircraft include:
Uniform surface attack. This is the most common type and is caused simply by
exposing the metal to oxygen in the air, such as when paint is worn off wing skin or
the fuselage. Poor pre-paint preparation at the factory, fumes, acid, pollutants, or
high humidity accelerate the decay.
Intergranular corrosion. Normally worst on 7000-series alloys (those with an
appreciable amount of zinc, like wing spars, stringers and other high-strength aircraft
parts), this is not frequently found but is a particularly nasty type of corrosion. It can
be difficult to detect, and once you see it, it’s too late: that piece of metal is toast.
Stress corrosion. In highly stressed parts like landing gear or engine crankshafts,
this type may develop from a scratch or surface corrosion. Crankshaft failures are
often due to undetected corrosion of this type.
Crevice or deposit corrosion. This can occur anywhere there is an area where
moisture or other pollutants are trapped. Lapped skin joints or rivets on an oil-stained
belly are examples of prime corrosion spots.
Filiform corrosion. Particularly on aluminum surfaces poorly prepared for
polyurethane paints, this type of corrosion will show up as fine, worm-like lines of
corrosion under the paint that will eventually lead to bubbling and flaking.
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Corrosion is an evil disease. It can strike aircraft young or old — although it definitely preys
more widely on the elderly — and can leave its damage unseen. Left unchecked, corrosion
can destroy an otherwise fine airplane and turn it into an unairworthy hulk. With the age of
the general aviation fleet, the effects of this deterioration have become ever more acute.
Few manufacturers building aircraft in the 1950s and 1960s could have predicted that their
products would still be in use so close to the year 2000; indeed, few prepared the structures
for such a long haul. Corrosion on aircraft is nothing more than rust of the metal parts,
although aluminum corrosion doesn’t produce the reddish color most people think of as rust.
Rather, it usually first shows as a whitish or gray “dulling” of the aluminum surface, then
progresses to more and more severe pitting and eventual destruction of the metal. Left
untreated, corrosion can make an aircraft unairworthy in just a few years. In spite of much
advancement in the science and technology of corrosion prevention and control,
the phenomenon of corrosion (usually of metals and alloys) continues to pose a
major concern to many industries around the world. The direct and indirect cost of
corrosion is huge (estimated to be US$2.2 trillion annually in direct costs
worldwide) (WCO, 2011). A good portion of the loss can be avoided by
proper corrosion control and monitoring.
In general, corrosion can be prevented by suitable modifications in: material (e.g.
selection of corrosion resistant materials), environment (e.g. addition of inhibitors)
and material surfaces (e.g. coatings). Metals can be protected cathodically (e.g.
cathodic protection) as well as anodically (e.g. passivation). In practice, effective
corrosion control is achieved by combining two or more of these methods.
