Which of the following is corrodes faster?Iron pole in sea water or iton pole on the beach?Ans) There are various ways of reducing and preventing this form of corrosion.
One way is to electrically insulate the two metals from each other. Until they are in electrical contact, there can be no galvanic couple set up. This can be completed using plastic or another insulator to separate steel water pipes from copper-based fittings or by using a coat of grease to divide aluminium and steel parts. Use of absorbent washers that may retain fluid is often counter-productive. Piping can be isolated with a spool of pipe made of plastic materials or made of metal material internally coated or lined. It is important that the spool has a minimum length of approx 500 mm to be effective.One more way is to keep the metals dry or shielded from ionic compounds (salts, acids, bases), for example by painting or encasing the protected metal in plastic or epoxy, and permitted them to dry. Coating the two materials or if it is not possible to coat both, the coating shall be applied to the more noble, the material with higher potential. This is essential because if the coating is applied only on the more active material, in case of damage of the coating there will be a large cathode area and a very small anode area, and for the area effect the corrosion rate will be very high.
It is also possible to choose metals that have similar potentials. The more closely matched the individual potentials, the lesser the potential difference and therefore the lesser the galvanic current. Using the same metal for all construction is the most precise way of matching potentials. Electroplating or other plating can also help. This tends to use more noble metals that resist corrosion better. Chrome, nickel, silver and gold can all be used. Galvanizing with zinc protects the steel base metal by sacrificial action.