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Types Of Corrosion

While there are a number of forms or types of corrosion, it is rare that a corroding structure or component will suffer from only one. While some forms of corrosion may be unique they are all interrelated.

UNIFORM CORROSION
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The most common form of corrosion. Found in ferrous metals that are unprotected by a surface coating corrosion preventive compound. Corrosion is in the form of a uniform layer of “rust” on the surface where the metal becomes thinner and will eventually fail. This is the most common type of corrosion, and from a technical point, the best understood.

GALVANIC CORROSION
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Occurs because of the potential differences between two or more different metals when they are in contact and exposed to an electrolyte, such as dissimilar metals in direct contact with each other and with salt water. Corrosion occurs at the anode. Any mechanical damage such as scratches on anodized aluminum and Galvanic corrosion will quickly eat through the metal.

HYDROGEN INDUCED CRACKING
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Results in the brittle failure of otherwise ductile or malleable materials when exposed to an environment where hydrogen can enter the metal. This is a common problem in processes or conditions involving wet hydrogen sulfide such as in oil fields.

CREVICE CORROSION
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A microscopic crack or crevice where materials meet, either metal-to-metal or metal-to-nonmetal materials such as a gasket, that is filled with moisture which then becomes de-oxygenated and undisturbed by the surrounding environment allowing corrosion to take place.

SELECTIVE LEACHING OR DE-ALLOYING

is a corrosion process in which one constituent of an alloy is removed preferentially, leaving an altered residual structure.

STRESS CORROSION CRACKING

Occurs in metals exposed to repetitive high tensile stresses and the presents of a corrosive medium such as salt water causing fine cracks to develop through the metal.

FRETTING CORROSION
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Defined as metal deterioration caused by repetitive slip or movement at the point where two surfaces come in to contact and move against each other. The two surfaces   were not intended to move in that fashion.

CORROSION FATIGUE
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Caused by the combined action of a repeated cyclic tensile stresses such as aircraft landings and a corrosive environment such as sea water.

STRAY VOLTAGE CORROSION
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Very similar to galvanic corrosion however the current amplitude is generally higher than that produced in galvanic corrosion and the corrosion much more rapid.

INTERGRANULAR CORROSION

The preferential attack at, or adjacent to, the grain boundaries of a metal. Intergranular corrosion causes the alloy to disintegrate and loses its strength.  Exfoliation corrosion is visible evidence of intergranular corrosion and most often seen on extruded sections where grain thickness is less than in rolled form

PITTING CORROSION

A deep, focused attack that can cause rapid penetration of the metal. Pitting is one of the most destructive forms of corrosion. It is also difficult to detect because of the generally small size of the pit or hole.

MICROBIAL CORROSION

Caused by specific types of microbes or bacteria’s waste in an otherwise benign environment which can lead to corrosion.

EROSION OR FLOW CORROSION

Caused by the corrosive fluid flowing through an unprotected metal surface such as a pipe.

Corrosion is a serious problem for industry and governments worldwide. 
Read our article “Corrosion Control Solutions – A Solution To A Costly Problem”
for details about the enormity of the costs involved in failing to prevent corrosion.

 


CORR-EX, LLC - Corrosion Prevention And Control

216 King Cotton Road
Brunswick
GA 31525

CAGE Code: 6MWZ4

 

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website last updated July 2016
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