Galvanization (or galvanisation) is the process of applying a protective zinc coating to steel or iron, in order to prevent rusting.In few services care should be taken to avoid rusting of the pipeline as it might be hazardous to personnel, cause damage, malfunction of equipment, instrument, etc. so for that reason the piping is galvanized.
The most commonly used methods for galvanization is hot dip galvanizing and electro-galvanizing.
Below are the differences between Hot dipped galvanization and Electro-galvanization. And advantages of one over the other-
|
Hot dip galvanization |
Electro-galvanization |
| Stringent cleaning procedure is followed (usually termed as 7-bath process: cleaning in alkaline solution, water rinsing, pickling, water rinsing, pickling, water rinsing, fluxing). | Stringent cleaning procedure is not usually followed. |
| Steel is dipped into the molten bath of Zinc @460ºC for achieving the coat | Steel is made the cathode in the electrolytic cell there by forming the coating by Electroplating process |
| Produces a Fe-Zn alloy layer on the steel surface and leaves a coat of pure zinc on the outer surface. The alloy is very hard. Usual abrasion does not damage the coating although it may damage the soft pure zinc on the top | Produces a layer of Zn on the surface which is not continuous with steel metallurgically |
| Very high life, of the order of 20-50 years | Very low life, few months to few years |
| Dull finish and usually is not very pleasant | Good finish |
| Normally coating thickness is 80-100µm.Coating thickness depends on the duration of dipping. It is also affected by the composition & roughness of steel | Normally coating thickness is 10-12 µmCoating thickness depends on current density and temperature of the electrolyte |
| With normal coat thickness about 40% expensive than electro-galvanizing | With normal coat thickness cheaper in comparison to hot dip galvanizing. However at higher coating thickness the cost increases proportionately and hence become exceptionally expensive. |
| Non-uniform coating | Uniform coating |
| Suitable for any size | Suitable for small components |
| Specs: ASTM A123ISO 1461IS 2629BS 729 | IS 1573 |