Galvanized Iron (G.I) Sheet | HVAC Ducting

Do you have an Iron or steel sheet and want to increase its life cycle and make it protective, corrosion, and rust-free?

Galvanized Iron duct sheet is the best solution you can use in HVAC for ducting and many other mechanical industries.

 Let me help you clarify your concept about Galvanized Iron sheet and its main process, and how it works?

Which process is better?

What is a G.I Sheet?

G I sheet is also used in HVAC ducting.

The galvanized iron sheet is an abbreviation of G.I sheet. We use an iron sheet in mechanical engineering, especially in HVAC ducting and cladding, to make the HVAC system secure, protective and increase its life cycle.

The process of applying the layer of Zinc on the Iron or steel that process is called galvanization.

The layer we apply to protect it and increase its life cycle is Zinc.

Yes, you heard right.

 We apply a layer of Zinc to overcome any accident and make it strong to work properly with the proper life cycle without damage.

Galvanized Iron Sheet for HVAC Ducting & Cladding

The question is,

Why should we use Zinc instead of other metals or materials?

The answer to this question is that Zinc has a low affinity, especially when it comes to weather conditions compared to other metals. That is why it is efficient and protects Iron or steel from rusting and damaging.

Zinc is also a better surface finisher material. So, it increases the life cycle of iron and steel sheets and makes them strong.

What is the History of the G.I Sheet?

The History of Galvanized Iron sheet started in the 17th century when LUIGI GALVANI was an Italian physician, physicist, philosopher and biologist, and pioneer of bio-electromagnetics.

He also discovered animal electricity. Once he was working on frog legs, and he introduced galvanization.

Furthermore, In 1800 ALESSANDRO VOLTA proceeds Galvani study and proved the concept of galvanization.

History of Galvanization or G.I Sheet

What are the two main processes of the G.I sheet?

Galvanization is a process that has to pass from many steps.

The Main two processes of galvanization, which are very common and famous, are mentioned below.

  • Electro-galvanized process
  • Hot dip-galvanized process

Let’s discuss each process in detail to understand it better and clear misconceptions regarding galvanization.

What is the Electro-galvanized process of the G.I sheet?

In the electro galvanization process, one metal will be coated with another metal by electrolysis.

One metal is Zinc, and another might be Iron or Steel sheet.

The metal we have to coat to another metal is placed as an anode (+ve), and the metal which will be coated with Zinc that might be steel or Iron sheet that will be placed and act as the cathode (-ve).

So, in the electro-galvanized process Anode (+ve) will be Zinc, and cathode (-ve) will be Iron or steel sheet.

Both metals react with each other in the electrolysis process, and reaction forms between them; as a result, galvanization occurs, and Zinc will be dissolved and coated on an Iron or Steel sheet.

The question is,

How does this electrolysis process of galvanization work?

In a Jar, we will take an electrolyte solution in liquid form. The solution we will take to start the reaction is zinc salt because we are coating Zinc on an iron or steel sheet.


Suppose we want to coat another metal like Aluminum on a steel or iron sheet. In that case, we have to take an electrolyte liquid as Aluminum.

I hope now you are clear about the misconception of the Electrolyte solution.

We will give power supply to Anode and cathode with positive and negative charges.

When we give power, electrons will transfer from Anode (+ve) to the cathode (-ve), but current will flow against the flow of electrons from the cathode(-ve) to Anode (+ve).

Zinc metal from Anode (+ve) will be dissolved gradually during the reaction. And during the reaction, Iron or steel will be coated with Zinc.

Once the coating is implemented, we will close the electrolysis process and get our galvanized Iron sheet.

I hope your concept of electro-galvanization is cleared now.

Let’s discuss another process of galvanization.

Galvanization Processes

What is the Hot-dip galvanization process?

In the Hot dip-galvanization process, the metals that can easily melt at low temperatures, such as Zinc, Aluminum, chromium, and cadmium, can be used to coat iron or steel metals.

These low-temperature metals are always coated on high-temperature-based metals like Iron and steel.

The end goal of this process is also to protect and prevent corrosion and to rust and increase its life cycle.

The sheet we have to coat might be an iron sheet or steel sheet; firstly, we always do some surface preparation.

Once surface preparation is completed, we have to transfer it for the next step of coating Zinc.

Here are some steps of the Hot dip-galvanizing surface preparation process. Let me know you one by one.


The first step of surface preparation is degreasing.

Degreasing is a process in which we remove Fat, Oil, and grease from the metal sheet.

Degreasing can be done by polishing it with a solution of lemon juice, baking soda, or vinegar, to name a few.


Iron or steel metal sheets will be washed with water and dried with fresh air in this process.

This process is used to remove contaminants from the surface.


In the pickling process, we will dissolve the sheet in dilute sulphuric acid (H2SO4), which helps to remove dirt, impurities, or scales from the sheet.

After doing pickling again, the process of rinsing is revised, and clean it with water and dry it.

Flux solution

Before dissolving the metal in Zinc, there is a layer on the upper surface of the zinc solution; that layer of solution is known as flux solution.

 The Iron or steel metal will be dissolved in the flux solution, basically a mixture of Aluminum chloride and zinc chloride.

It protects the formation of oxygen to prevent spots of oxygen; that’s why we have to dissolve it from flux solution.

Here the process of surface preparation is going to end.

Dissolving metal into Zinc

Now, the Iron or steel sheet can be dissolved in Zinc or any other low-temperature metal to make the Iron or steel sheet protective, strong, and corrosion-free.

Cooling and inspection

It is the last step of the Hot dip-galvanization process in which we analyze the metal and cut excessive zing from the metals with the help of rollers and cutters.

Cool it, and after cooling, we will send it for inspection to get a better result.

The question is,

How can we know which galvanization process will be effective and better for us?

To know which process is effective and has a high life cycle, here is a process called the Salt spray test process.

It will help you to know which galvanization process is more effective and has a higher life cycle.

What is a Salt Spray Test?

It is a test that will tell us which galvanized sheet is better or which galvanized process is efficient.

Salt Spray Test for Galvanization

How to do a salt spray test?

We mix salt with water and then spray the whole G.I sheet size on the coated metal or galvanization sheet and leave it for 27 hours. After 27 hours, you will see the result.

In most cases, Electro galvanized process sheets will get corrosion, and Hot-dip will be the same.

The results show that the Hot dip-galvanized process is more efficient than the electro-galvanized process.

Note: Finishing of Hot-dip galvanization is rough, and Electro galvanization is shiny.

 So it does not mean that electro galvanization is pure.

Here is a famous saying that “Every Shiny Thing is not gold,” so be secure.

Yes, Hot-dip galvanization is expensive, but it is also efficient and better than electro-galvanized sheets.

Do you know you can easily know by visualizing a sheet which galvanized sheet is better?

Yes, If a sheet is too shiny and doesn’t have any spangle, it’s a low-quality galvanized sheet.

Note: Higher the spangle Better the sheet.

During the installation process of galvanization in the mechanical industry, the testing of galvanization occurs from which we can get to know which is an industry-standard based.


Galvanized sheet is best if you are using it for ducting and in HVAC or any mechanical use; it will help you increase the life cycle of an Iron or Steel it and prevent corrosion and rusting.

So I will suggest you use a high-quality Hot-dip- galvanizing sheet. Yes, the gi ducting sheet price is high, but it will not only protect you better and not get any corrosion or rusting.

Don’t be a black sheep, don’t judge a book by its cover, and don’t judge a sheet by its shining surface. If a surface is shiny means, the sheet is low galvanized.

Always test it with a salt spray test before purchasing and choose a sheet that has more spangles.

FAQ (Frequently Asked Questions)

If a Sheet will get any spot of water and preparation, can it be removed or not?

It cannot clean; if you clean it, then the galvanization layer will be no more. It is suggested to apply anti-corrosion silver paint on affected spots.

Should we wash vegetables in a galvanized Iron tank?

According to the American galvanizers association, you can use it for vegetables but not for acidic food. Acidic food always reacts with Zinc.

I hope My Article will help you a lot.

If you have any questions regarding it, please be the first to comment.

You can watch my G.I Sheets videos in Urdu/Hindi language for more detail or easy understanding

Galvanized Iron Sheet, Part-1
Galvanized Iron Sheet, Part-2
Galvanized Iron Sheet Inspection, Part-3

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