Fretting Corrosion
Fretting Corrosion
When surfaces move in relation
to each other, this relative motion can result in abrasion. This abrasion can increase
the attack at these fraying surfaces.
Definition.
Fretting corrosion is an attack
that is accelerated by the relative motion of contacting surfaces.
Mechanism.
Fretting corrosion is usually
a combination of
corrosion and abrasive wear. The motion between the surfaces removes
protective films and results in accelerated attack. Also, most corrosion products
are abrasive and their presence increases the removal of protective films and in
direct abrasion of the metal.
Examples.
Fretting was common in riveted
joints on ships and other riveted structures where cyclic loads were experienced,
but this has largely been eliminated through welded construction. Fretting is, however,
still encountered in bolted joints and flanges where there is not enough bolt tension
to eliminate movement in the joint. Thermal expansion with frequent cycling can
also result in fretting attack. Any combination of corrosion and wear will almost
always be worse than the action of either one separately.
Appearance.
Fretting corrosion usually results
in scuffed surfaces in joints or at other wear sites. If inspected soon after the
relative motion ceases, the surfaces will often be bright and have corrosion products
attached to the surfaces.
Significant Measurements.
There are no standard tests for
fretting corrosion. When encountered, it is addressed through mechanical design
rather than material selection. Where it cannot be eliminated it can sometimes be
reduced by using inhibitive caulking compounds in the joints.
