• Corrosion may be broadly defined as the degradation of a
material due to interaction with its environment.
deterioration of metals and alloys by chemical or electrochemical
reverse process of extractive metallurgy.
Physico-chemical interaction between a metal and environment
16. Degradation of Metals
In metals, there is actual material loss either by dissolution or by the formation
of nonmetallic scale or film (oxidation).
The problem of metallic corrosion is one of significant proportions.
In economic terms, it has been estimated that approximately 5% of an
industrialized nation’s income is spent on corrosion prevention and the
maintenance or replacement of products lost or contaminated as a result of
METALLIC CORROSION --- ELECTROCHEMICAL REACTIONS
Hence, corrosion is a surface phenomena which interaction of metals with its environment by
electrochemical, chemical and physical depending upon the involvement of the electrons, ions
17. Deterioration of Polymers
• Polymers may deteriorate by swelling and dissolution.
• Covalent bond rupture, as a result of
• It should also be mentioned that because of the chemical
complexity of polymers, their degradation mechanisms are not well
POLYMERIC CORROSION ---- PHYSIOCHEMICAL
18. Deterioration in Ceramics
• Ceramic materials are relatively resistant to deterioration, which
usually occurs at elevated temperatures or in rather extreme
• Corrosion of ceramic materials generally involves simple chemical
19. Major Consequences of corrosion
• Reduction of metal thickness leading to loss of mechanical strength and structural failure or
• Hazards or injuries to people arising from structural failure or breakdown (e.g. bridges, cars,
• Loss of time
• Reduced value of goods due to deterioration of appearance.
• Contamination of fluids in vessels and pipes.
• Perforation (small holes) of vessels and pipes allowing escape of their contents and possible
harm to the surroundings.
• Loss of technically important surface properties of a metallic component. These could
include frictional and bearing properties, ease of fluid flow over a pipe surface, electrical
conductivity of contacts, surface reflectivity or heat transfer across a surface.
• Mechanical damage to valves, pumps, etc, or blockage of pipes by solid corrosion products.
• Added complexity and expense of equipment.
23. CLASSIFICATION OF CORROSION
On the basis of electrolyte
a. Wet or Aqueous corrosion
b. Dry corrosion (oxidation in the absence of water)
On the basis of environment
a. Atmospheric corrosion
b. Underground corrosion
c. Marine corrosion
On the basis of temperature
a. Low-temperature corrosion
b. High-temperature corrosion
Sweet corrosion and Sour corrosion
24. ESSENTIAL COMPONENTS OF CORROSION
The four essential components of corrosion:
A metal dissolution process
Produce electrons /Lose of electrons
A metal deposition process
Consumption electrons /Gain of electrons
Ionic path between anode and cathode
Ionic species move through it (Anions and cations)
Electronic path between anode and cathode
Electron will pass through it
Fe = Fe2+ + 2e (Oxidation reaction )
2H+ + 2e = H
Fe + H2O = Fe (OH)2 (Redox reaction)
Corrosion of iron in de-aerated water
26. CORROSION COST
- Did you know that corrosion costs around $2.5 trillion dollars globally (3 to 4% of GDP of
- (Reference: Corrosion Awareness Day, April 24, 2017, organized by WCO)