Different types of corrosion observed in our surroundings Uniform Corrosion Corrosion Erosion Galvanic Corrosion Causes and Prevention practical example

1. Presented By:
Saad Bin Hasan
B.Sc. in Chemical Engineering,JUST
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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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9. Thank You
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