The various methods that can be used to protect a metallic
system against corrosion can be widely divided into:
Thermodynamic protection
This type of protection is based on
the requirement that the metals have a high positive value for the free energy
change for conversion of the metal to a corrosion product in the exposed
environment.
Kinetic protection
Corrosion rate of an actively
corrosion metal is determined by the intersection of the kinetic curves that
characterize the anodic and cathodic corrosion reactions. This type of
protection is based on the principle that the corrosion rate can be reduced if
either of these reaction can be changes such that the point of intersection is at
a lower current density.
Barrier protection
The concept of barrier protection is
to protect the metal from the environment by means of a barrier that resists
penetration by aggressive environmental constituents. Typical forms include,
anodic oxides, ceramic and inorganic coatings, inhibitors, organic coatings
etc.
Structural design
Structures should be designed such
that the length of time that a structure is wet with water is minimized. ;
Environmental control
This type of protection is limited
to closed systems in which changes in the composition of the medium can be
tolerated. The method depends of the removal of a constituent of the corrosion
reaction from the medium, or in some cases adding a component to a medium. ;
Metallurgical design
Use of the proper alloy for the
environment against which protection is sought is the principle behind this
form of corrosion protection.