Cathodic Protection

Corrosion is the destructive attack of a metal by chemical or electrochemical reaction with its environment. Deterioration by physical causes is not called corrosion,but is described as erosion, galling, or wear. In some instances, chemical attack accompanies physical deterioration, as described by the following terms:corrosion – erosion, corrosive wear, or fretting corrosion. Nonmetals are notincluded in this definition of corrosion. Plastics may swell or crack, wood may split or decay, granite may erode, and Portland cement may leach away, but the term corrosion, in this book, is restricted to chemical attack of metals.The series consequence  of corrosion process have become a problem of wide world significance , in addition to our every day encounters with this form of degradation .The three main reasons for the importance of corrosion are: economics, safety,and conservation.  Corrosion causes plant shut down, waste of valuable resources , loss or contamination of products , reduction in efficiency costly maintenance and expensive over design.  To reduce the economic impact of corrosion, corrosion engineers,with the support of corrosion scientists, aim to reduce material losses, as well as the accompanying economic losses, that result from the corrosion of piping, tanks, metal components of machines, ships, bridges, marine structures and so on. Corrosion can compromise the safety of operating equipment by causing failure (with catastrophic consequences) of, for example, pressure vessels,boilers, metallic containers for toxic chemicals, turbine blades and rotors, bridges,airplane components, and automotive steering mechanisms. Safety is a critical consideration in the design of equipment for nuclear power plants and for disposal of nuclear wastes. Loss of metal by corrosion is a waste not only of the metal, but also of the energy, the water, and the human effort that was used to produce and fabricate the metal structures in the first place. In addition, rebuilding corroded equipment requires further investment of all these resources metal, energy, water, and human.
Corrosion took different forms uniform , pitting , crevice , intergranular , stress corrosion cracking , fatigue , and other forms , and it is affect on metals and alloys by combination operating condition (i.e. temperature , aggressive species concentration , ect.).Despite different definitions, it can be observed that corrosion is basically the result of interaction between materials and their environment. Up to the 1960s, the term corrosion was restricted only to metals and their alloys and it did not incorporate ceramics, polymers, composites and semiconductors in its regime. The term corrosion now encompasses all types of natural and man-made materials including biomaterials and nanomaterials, and it is not confined to metals and alloys alone. The scope of corrosion is consistent with the revolutionary changes in materials development witnessed in recent years