01 March 2005
Metal Ions Go Into Solution
From the Anode
Dissimilar Metal Contacts
3-8.10. MECHANICAL STRESS. Many alloys used in
3-8.8. T E M P E R A T U R E . H i g h e r t e m p e r a t u r e
aircraft construction are sensitive to a form of corrosion
environments tend to produce more rapid corrosion due
known as stress corrosion cracking. Manufacturing
to accelerated chemical reactions and, in humid
processes such as machining, forming, welding, or heat
environments, higher concentration of water vapor in
treatment can leave residual mechanical stresses in
the air. In addition, nightly drops in temperature can
aircraft parts. The addition of in-service stresses to
residual stresses can cause corrosion to proceed more
increased corrosion rates.
rapidly than would be expected in normal service.
3-8.11. LENGTH OF EXPOSURE. As time passes,
fungi, and other living organisms (some microscopic)
metals naturally tend to corrode. In some cases, the
can grow on damp surfaces. Once they are well
corrosion process occurs at the same rate, no matter
established, the area tends to remain damp, increasing
how long the metal has been exposed to the environment.
the possibility of corrosion. Their presence can cause
In other cases, corrosion can decrease with time, due to
the areas they occupy to have different oxygen and
the barrier formed by corrosion products, or increase
electrolyte concentrations. In addition, acidic wastes
with time if a barrier to corrosion is being broken down.
are secreted, which cause corrosion.