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Form of Corrosion

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الكلية كلية الهندسة/المسيب     القسم هندسة السيارات     المرحلة 3
أستاذ المادة جعفر هادي عبود المياح       31/10/2018 12:47:25
Forms of corrosion
General corrosion
This corrosion form is also referred to as general
corrosion, it results from a chemical attack that
proceeds at a similar rate over the entire surface. Typically the atmospheric exposure ofiron metals (if not specifically corrosion resistant alloys) leads to the formation of red rust (see corresponding picture). Metals like stainless steel
or aluminium can oxidise and form a protective oxide layer that hinders the progression of the corrosion reaction.
Galvanic corrosion
At least two dissimilar metals or alloys must be electronically connected in general electrolyte. In
this case the metal that oxidises in favour of the more cathodic one is lower on the galvanic series.
The mode of action is analogous to a battery cell. Thus, the higher the current that flows in the
system the severer the corrosion. This form of corrosion is very common in water pipes where
tubings of steel and copper or copper containing alloy are joined.
Crevis Corrosion
This form of corrosion occurs within crevices and other shielded areas on metallic surfaces that are
exposed to a corrosive environment. Typically, crevices can develop a local chemistry that is different from that of the bulk fluid, especially when stagnant solutions can remain in this crevices. The contact area of metallic and non-metallic surfaces may be attacked by this form of corrosion.

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