The loss to the world economy due to corrosion is in the billions per year. This loss is due to, galvanic corrosion, direct attack corrosion, and other types of corrosion. A rusty bolt on a machine could shut down a production line for hours, or even days. Its the old age problem of corrosion. There are steps you can take to minimize the problem. Assess the environment where your investment will be, and use the proper corrosion-resistant fastener accordingly. At Clark Craft, we supply fasteners in corrosion-resistant metals. In the long run, when you consider the labor, maintenance, and replacement cost of a failed fastener, the cost would have been far less if the proper fastener had been used.
is corrosion? Corrosion is the wearing away, or alteration of a metal
by galvanic reaction, or by direct chemical atttack. An example is the
rusting of iron, or steel.
Galvanic Corrosion (Electrochemical). All metals have specific relative electrical potential. When metals of different electrical potenial such as steel and copper are in contact in the presence of moisture, a low energy electric current flows from the metal having the higher position in the galvanic series.This is called "galvanic action."
To help prevent direct attack corrosion. Select the material most likey to resist the corrosive environment to which the fastener will be subjected.
To help prevent galvanic
corrosion. If possible use the same, or similar metals in an assembly,
especially where an electrolyte may be present. ( One example of an electrolyte
would be water). When dissimilar metals are used together in the presence
of an electrolyte, separate them with a dialectric material such as insulation,
paint or coating. Avoid combinations where the area of the less noble
material is relatively small. The current density is greater when the
current flows from the small area to the large rather than in the reverse
situation. Typically, the fastener will be small compared to the rest
of the assembly. The fasteners alloy, if not the same as the material
being joined, should be lower in the galvanic series. The galvanic process
can be used to your advantage by coupling the part to be protected to
pieces of less noble metal which are not functional and can thus corrode
sacrificially. An example of this would be a zinc fastened to the strut
on a yacht in sea water.