2. Corrosion types

Corrosion can be divided into different groups according to their form of occurrence.

General corrosion / uniform corrosion

Metal corrodes uniformly all over the surface.

Local corrosion

Part of the structure corrodes at a considerably higher than average rate.  The categories of local corrosion are:

Pitting corrosion

• the corrosion effect is concentrated on localised areas and leads to pitting.

Crevise corrosion

• proceeds at locations covered by a corrosion product and other deposits (dirt or trash). Crevice corrosion typically occurs in small cavities, gaps, recession, etc.

Galvanic corrosion

• galvanic corrosion requires two different metals, constituting a corrosion cell. A structure should contain metals that are as close to each other as possible in the galvanic electric series.

Intergranular corrosion

• intergranular corrosion proceeds along the metal grain boundaries.

Selective corrosion

• selective corrosion occurs, for example, when one element in an alloy dissolves faster than the others.

Combined effect of mechanical factors and corrosion

Mechanical wearing as well as static or dynamic stresses often act in combination with corrosion. The main categories for combined effect of mechanical factors and corrosion are:

Stress corrosion

• stress corrosion occurs when a metal in a corrosive environment is exposed to static stress that results in fracture.

Corrosion fatigue

• corrosion fatigue is caused by the combined effect of corrosion and varying state of stress.

Erosion corrosion

• erosion corrosion is an acceleration in the rate of corrosion caused by high velocity of a liquid, or solid impurities carried by a liquid.

Cavitation corrosion

• cavitation corrosion is erosion caused by the combined effect of corrosion and the pressure caused by the breaking of gas bubbles formed in liquid (cavitation). .

Fretting corrosion

• fretting corrosion occurs between two metals rubbing against each other under corrosive conditions.

• << Prev
• Next >>