(i) Barrier protection:
In this method, the surface is coated with some impermeable layer such as paint or oil greasing to prevent the access of damp air.
The surface is coated electrolytic ally with a metal which will not be oxidised easily, e.g., electroplating of nickel, chromium, tin etc., on articles to be protected.
(iii) Sacrificial protection:
In this case coated metal gets corroded in preference to the one which is protected. For example, iron sheets are coated with zinc (Galvanisation). Here even if the coating gets punctured, zinc will be preferentially oxidised.
(iv) Cathodic protection:
This is the most elegant method. The metal to be protected (say an iron tank) is made the cathode either by connecting to external power source or to a more active metal like magnesium.