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Types of Corrosion 2

Published on March 2017 | Categories: Documents | Downloads: 5 | Comments: 0
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Morphology of pitting
Subsurface pits
Undercutting pits
vertical grain attack
Horizontal grain
attack

A pitting-related accident
The sewer explosion that killed 215 people in Guadalajara,
Mexico, in 1992. Besides the fatalities, the series of blasts
damaged 1,600 buildings and injured 1,500 people.
Damage costs were estimated at 75 million U.S. dollars.

Crevice corrosion
Crevice corrosion is a localized form of corrosion usually
associated with stagnant solutions in shielded areas such
as those formed under gaskets, washers, insulation
material, fastener heads, surface deposits, disbonded
coatings, threads, lap joints, clamps, etc.

Example of crevice corrosion


Crevices
corrosion of a
S30400
stainless steel
washer after 30
days in 0.5
FeCl3 + 0.05 M
NaCl solution

Another example of crevice
corrosion

Stainless steel bolt used in seawater after 5 years of
exposure.

Initiation of crevice corrosion
Crevice corrosion is initiated by changes in local
chemistry within the crevice:
– Depletion of inhibitor in the crevice
– Depletion of oxygen in the crevice
– A shift to acid conditions in the crevice
– Build-up of aggressive ion species (e.g. chloride) in the
crevice

Popped rivets found on an
external section of a
maritime patrol aircraft
fuselage.

Analysis of a crevice-corrosion
related problem (popped rivets)







Subsequent inspection revealed corrosion in the bonded
area of the skin plates.
The cause was believed to be water ingress from a global
positioning system (GPS) antenna.
It was believed that water penetrated through cracks in the
seal surrounding the GPS antenna.
Once the water was in, crevice corrosion began and it
ultimately led to the loss of the bond between the two
portions of the structure.
The loss of this bond allowed more water to seep in the
structure and generalized the corrosion problem.

Analysis of a crevice-corrosion
related problem (continued)



Underside of panel where severe corrosion was found

Analysis of a crevice-corrosion
related problem (continued)

Close-up picture showing the severity of corrosion

Advanced crevice corrosion
“pillowing”

Notice how the rivet heads appear to be lower than the
surrounding skin surface.

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