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CORROSION CONTROL AND PREVENTION - Coggle Diagram
CORROSION CONTROL AND PREVENTION
Materials selection
Selection of proper material for a particular corrosive service.
Modify the properties of material
Metallic materials
Use proper metal for particular environment
Ex: Metal and alloy
Nonmetallic Materials
Limit polymer use in the presence of inorganic acids
Ex: rubbers (natural and synthetic)plastics, ceramics, carbon and graphite, and wood
Modify the Environment
Controlling the environment
Controlling the relative humidity:
%RH < 50% most metal such as Al, Cr and Ni will less corrode.
Removal of oxygen:
By the removal of oxygen from water systems in the pH range 6.5-8.5 one of the components required for corrosion would be absent
Controlling pH, temperature, pressure, velocity, ionic contaminants and etc.
Use of inhibitor
Definition:
in general terms as a substance which, when added in a small concentration to an environment, effectively reduces the corrosion rate of a metal exposed to that environment.
Mixed inhibitor
- An inhibitor that acts both in a cathodic and anodic manner.
E.g. chromate/polyphosphate
Anodic inhibitor
- forms a passivation layer on aluminium and steel surfaces which prevents the oxidation of the metal.
E.g. Chromate, nitric, borate
Cathodic inhibitor
- retards the corrosion by inhibiting the reduction of water to hydrogen gas (inhibit the reduction processes).
Ex: zinc salts, Magnesium salts
Protective coating
Metallic coatings
protect metal by separating from corrosive environment and the coating serve as sacrificial anode.
For example a protective zinc coating is galvanized to steel or iron, to prevent rusting.
Non metallic coatings
Organic coatings
Protect metal surface by polymer (paint and vanishes)
Inorganic coatings
Protect steel or metal surface with layer of porcelain or glass
Cathodic and Anodic Protection
Cathodic Protection
Electrons are supplied to the metal structure to be protected
Anodic Protection
Externally impressed anodic currents form protective passive films on metal/alloy surfaces.
Proper Design
Avoid dissimilar metals that can cause galvanic corrosion.
Provide allowance for corrosion in thickness
Avoid excessive stress and stress concentration
Avoid sharp bends in pipes to prevent erosion corrosion
