CORROSION / WEEPING of METAL

CORROSION is defined as the deterioration or destruction of metals and alloys in the presence of an environment by chemical or electrochemical means.

# Also said as reaction of metal with the environmental species.

# ( IUPAC ) Is an irreversible inter-facial reaction of a material with its environment, which results in consumption or dissolution into the material of a component of the environment.


CLASSIFICATION

• Chemical and Electrochemical
• Wet and Dry 

TYPES OF CORROSION

• UNIFORM CORROSION - occurs on the whole surface.
• PITTING CORROSION - occurs in the local pits on a surface.
• CREVICE CORROSION - occurs on the grooves when bolts are present.
• GALVANIC CORROSION - occurs when two metals come in contact, and the reactive metal gets corroded leaving the other metal safe.
• ENVIRONMENTAL CORROSION - occurs due to bad harsh conditions.
• STRESS CORROSION - occurs due to severe stress causing damage to the metal.
• FRETTING CORROSION - due to repeated wearing off of the machinery components.

FACTORS CAUSING CORROSION

• Oxygen
• Moisture
• Reactivity of the metal
• Electrolyte presence
• Galvanization
• Pollutants like NO2 CO2.
• High temperature
• Surface ( Rough or Smooth ) Nature
• Humidity

PREVENTION FROM CORROSION

• Electroplating - coating with another metal with help of electricity.
• Barrier protection - with paints and enamels.
• Rective Coating - coating with a more reactive metal which gets corroded ( Sacrificial ).
• Anodization - Electrochemical method of depositing an inert and stable oxide layer which is more durable and decorative ( Aluminium ).
• Cathodic Protection - A more reactive metal is attached via wire, to the underground pipelines and tanks, which by the principle of galvanization gets reduced and keeps the tanks safe.