It is defined as change in the properties of metal due to chemical reaction between metal and its Surrounding environment.here we will discuss corrosion and its types.
Or
It is defined as a destruction of metal or deterioration of metal due to chemical reaction with its environment.
Materials can be
- Metals
- Polymers
- Ceramics etc.
Fig 1. Corrosion
CORROSION AND ITS TYPES
- GALVANIC CORROSION
- PITTING CORROSION
- CREVICE CORROSION
- HIGH TEMPERATURE CORROSION
Galvanic corrosion
Galvanic corrosion occurs when there is physical or chemical contact between two dissimilar metals in the presence of an electrolyte.
Pitting corrosion
Pitting corrosion is the formation of cavities on the material surface. it occurs when there is cavity or hole forms on the material metal surface. it is most damaging and difficult to detect fact that.It is small in size usually.
Crevice corrosion
Crevice corrosion occurs in confined space, contact of metals with metals where access of fluid from environment is limited due limited gaps and contact area between parts.
Examples are
- under gasket
- bolts and lap joints
- screws and fasteners
High temperature corrosion
It is the degradation of a metal due to the heating. Degradation implies deterioration of physical properties of the material. it occurs when metal is subjected to a hot atmosphere cause oxidizing the material due to presence of oxygen , sulphur or other compound.
Corrosion control
- surface treatments
- cathodic protection
- hot dip galvanizing
Surface treatments
Surface treatment occurs by applied coatings .surface of metal can be protected by plating, painting.
These are most common anti corrosion treatments
Other surface treatment controls are
- Reactive coatings
- Anodizing
Cathodic protection
Sacrificial anode is type of cathodic protection.it is an electrical type of corrosion control.
Sacrificial anode comes in three metal
- Magnesium
- Aluminium
- zinc
Most widely used for steel protection is zinc .zinc and aluminium are usually used in salt water .
The rate of corrosion in the presence of zinc is generally slower.
It is generally uses for offshore pipelines, ships and boats, marine engines.
Hot dip galvanizing
Hot dip galvanizing is process in which steel sheet or strip is pass through pot contains the molten zinc at particular temperature. And there is zinc coating of sheet takes place. hot dip galvanizing resist corrosion .