Definition of Galvanization/ Galvanization Meaning
Galvanization or Galvanizing is one of the most widely used manufacturing processes of applying a thin zinc coating over steel or iron material for the purpose of protecting them from corrosion or rusting. Once this is done the steel or iron is called galvanized steel or galvanized iron. That zinc coating (silver color) in galvanized material shields (barrier) the metal from the surrounding environment. Thus galvanization extends the life of the base metal (Steel) to a considerable extent. That zinc coating is applied in several layers as per requirement.
In corrosive environment, Galvanized Steel is one of the cost effective alternative solutions to avoid using costly materials like SS or DSS. Galvanizing also prevent the metal from “galvanic corrosion” as the Zinc layer acts as an anode and slowers the corrosion tendency of the base metal.
Methods of Galvanization/ Galvanizing Methods
Galvanization is achieved by various methods as listed below:
- Hot-Dip Galvanization
Hot-dip galvanization process provides long-lasting, maintenance-free metal at cheap cost and the process is quite simple. In the Hot-Dip Galvanizing process, the base metal is dipped into a pool of molten zinc. Fig. 1 shows the steps involved in the complete process. There are three major steps that are followed in the hot-dip galvanizing process.
- Surface Preparation
- Fluxing and
- Galvanizing and
- Post-Process Treatment.
In the Electro-galvanizing process, Zinc ions are transferred to the base metal bu utilization of an electrical current source in an electrolyte solution. Electro-galvanizing is normally applied continuously.
Pre-galvanizing is performed at the steel mill, usually on materials that already have a specific shape. After cleaning, The metal is passed through a pool of hot molten zinc similar to hot-dip galvanization process and then recoiled. This method offers large scale galvanization.
Galvannealing is basically a combination of two methods; hot-dip galvanization and annealing. This method produces a specialized high quality coating on steel. The process involves hot-dipping and then instantaneous annealing, to produce a matte gray finish.
The codes and standards those govern the galvanization process are listed below:
- ISO 1461
- EN ISO 14713-1 & 2
- BS 7371-Part 6
- EN 10348‑2
- BS 3083
- EN 15773
- ASTM A123/A123M
- ASTM A153/A153M
- ASTM A767/A767M
- CSA G164
- ASTM B6
- ASTM A143/A143M
- ASTM A384/A384M
- ASTM A385/A385M
- ASTM A780
- ASTM D6386
- ASTM D7803
- ASTM E376
Need for Galvanized Steel Pipes
There are various services where 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. Galvanized pipes can work satisfactorily for up to 70 years. The other advantages that galvanized steel pipe (Fig. 2) offers are
- Reduced cost as compared to stainless.
- Very Less maintenance which results in the lowest long term cost.
- Highly Durable. Hence, Long life expectancy.
- Reliable performance.
- Resistance to mechanical damage.
- Good protection for rusting and galvanic corrosion.
However, for piping application only one disadvantage is that galvanized pipes can not be welded. So, clamped supports are used for galvanized piping systems.
Difference between Hot-dip Galvanization and Electro-Galvanization
Below are the differences between Hot-dipped galvanization and Electro-galvanization. And the 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).||Cleaning Procedure is not Stringent.|
|Governing codes and standards are ASTM A123; ISO 1461; IS 2629 or BS 729||IS 1573 governs the Electro-galvanization process|
|Highly Durable; of the order of 20-50 years||Comparatively low life|
|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|
|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|
|The surface finish is not smooth, dull finish.||Good surface finish|
|Depending on the dipping duration, the coating thickness is 80-100µm. It is also affected by the composition & roughness of steel||Normally coating thickness is 10-12 µm.|
Coating 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|
Hot-Dip Galvanization Video Tutorial
The following hot-dip galvanization video tutorial by American Galvanizers Association clearly explains the Galvanization process.