Different types of corrosion observed in our surroundings
Uniform Corrosion
Corrosion Erosion
Galvanic Corrosion
Causes and Prevention
practical example
2. Uniform corrosion is
the most common
type of corrosion and
is caused by a
chemical or
electrochemical
reaction that results in
the deterioration of
the entire exposed
surface of a metal.
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Fig: Uniform corrosion of corrugated
iron sheet.
3. CAUSES: PREVENTION:
Could happen in most
environments , such as dry
and wet atmospheres , acids
, brines, etc.
Could happen if metal is
improper, not coated or
galvanized, very active
metal, high temperature,
totally exposed to
environment.
Using less active metal.
Using coating.
Using inhibitor.
Using cathodic protection
Corrugated iron sheet have
to properly galvanized.
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4. Corrosion erosion is a
degradation of material
surface due to
mechanical action,
often by impinging
liquid, abrasion by a
slurry, particles
suspended in fast
flowing liquid or gas,
bubbles or
droplets, cavitation, etc
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Fig: Corrosion Erosion of metal pipe
5. CAUSES: PREVENTION:
Impinging liquid to surface
Fast flowing liquid or gas
Rough surface
Accumulation of water
droplet
High temperature Fluid flow
Cavitation
protective layer of oxide on
a metal surface is dissolved
by high velocity
Flow rate have to slow down
Have to confirm smooth
surface
Using inhibitor in fluid
Using low temperature fluid
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6. Galvanic corrosion occurs
when two different metals
are located together in a
corrosive electrolyte.
A galvanic couple forms
between the two metals,
where one metal becomes
the anode and the other the
cathode.
The anode, or sacrificial
metal, corrodes and
deteriorates faster than it
would alone, while the
cathode deteriorates more
slowly than it.
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Fig: Galvanic corrosion of a bicycle rim
7. CAUSES: PREVENTION:
Electrochemically dissimilar
metals must be present
(here Al & Cr)
The metals must be in
electrical contact
The metals must be
exposed to an electrolyte
Electrically insulate the two
metals from each other. If they
are not in electrical contact, no
galvanic coupling will occur.
Ensure there is no contact with
an electrolyte. This can be
done by using water-repellent
compounds such as greases,
or by coating the metals with
an impermeable protective
layer, such as a suitable paint,
varnish, or plastic.
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8. PREVENTION:
Choose metals that have similar electro potentials. The more closely
matched the individual potentials, the lesser the potential difference
and hence the lesser the galvanic current.
Electroplating or other plating can also help. This tends to use
more noble metals that resist corrosion better.
Cathodic protection uses one or more sacrificial anodes made of a
metal which is more active than the protected metal.
Cathodic Protection can also be applied by connecting a direct
current (DC) electrical power supply to oppose the corrosive galvanic
current.
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