Product Overview

CORROSION
All metal surfaces are affected by
corrosion. Depending on the physical
properties of the metal and the
environment to which it is exposed,
chemical or electromechanical corrosion
may occur
.
Atmospheric Cor
rosion
Atmospheric corrosion occurs when metal
is exposed to airborne liquids, solids or
gases. Some sources of atmospheric
corrosion are moisture, salt, dirt and
sulphuric acid. This form of corrosion is
typically more severe outdoors, especially
near marine environments.
Chemical Corrosion
Chemical corrosion takes place when
metal comes in direct contact with a
corrosive solution. Some factors which
affect the severity of chemical corrosion
include: chemical concentration level,
duration of contact, frequency of washing,
and operating temperature.
Storage Corrosion
Wet storage stain (white rust) is caused
by the entrapment of moisture between
surfaces of closely packed and poorly
ventilated material for an extended period.
Wet storage stain is usually superficial,
having no affect on the properties of the
metal.
Light staining normally disappears with
weathering. Medium to heavy buildup
should be removed in order to allow the
formation of normal protective film. Proper
handling and storage will help to assure
stain-free material. If product arrives wet,
it should be unpacked and dried before
storage. Dry material should be stored in
a well ventilated “low moisture”
environment to avoid condensation
formation. Outdoor storage is
undesirable, and should be avoided
whenever possible.
Galvanic Corrosion
Galvanic corrosion occurs when two or
more dissimilar metals are in contact in
the presence of an electrolyte (ie.
moisture). An electrolytic cell is created
and the metals form an anode or a
cathode depending on their relative
position on the Galvanic Series Table.
The anodic material will be the one to
corrode.
Anodic or cathodic characteristics
of two dissimilar metals will depend on the
type of each material. For example: If
zinc and steel are in contact, the zinc acts
as the anode and will corrode; the steel
acts as the cathode, and will be protected.
If steel and copper are in contact, the
steel is now the anode and will corrode.
The rate at which galvanic corrosion
occurs depends on several factors:
1.
The relative position on the Galvanic
Series Table - the further apart materials
are in the Galvanic Series Table, the
greater the potential for corrosion of the
anodic material.
2. The amount and concentration of
electrolyte present - an indoor, dry
environment will have little or no galvanic
corrosion compared to a wet atmosphere.
GALVANIC SERIES IN SEA WATER
Metals in descending or
der of activity in the pr
esence of an electr
olyte.
3. The relative size of the materials - a
small amount of anodic material in contact
with a large cathodic material will result in
greater corrosion. Likewise, a large
anode in contact with a small cathode will
decrease the rate of attack.
Magnesium
Magnesium Alloys
Zinc
Beryllium
Aluminum - Zinc Alloys (7000 series)
Aluminum - Magnesium
Alloys (5000 series)
Aluminum (1000 series)
Aluminum - Magnesium Alloys (3000 series)
Aluminum - Magnesium - Silicon Alloys (6000 series)
Cadmium
Aluminum - Copper Alloys (2000 series)
Cast Iron, W
rought Iron, Mild Steel
Austenitic Nickel Cast Iron
Type 410 Stainless Steel (active)
Type 316 Stainless Steel (active)
Type 304 Stainless Steel (active)
Naval Brass, Yellow Brass, Red Brass
Tin
Copper
Lead-Tin Solders
Admiralty Brass, Aluminum Brass
Manganese Bronze
Silicon Bronze
Tin Bronze
Type 410 Stainless Steel (passive)
Nickel - Silver
Copper Nickel Alloys
Lead
Nickel - Aluminum Bronze
Silver Solder
Nickel 200
Silver
Type 316 Stainless Steel (passive)
Type 304 Stainless Steel (passive)
Incoloy 825
Hastelloy B
Titanium
Hastelloy C
Platinum
Graphite
More Anodic
Anodic End
Cathodic End
Technical Data
Technical Data
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