Galvanneal vs Galvanized Steel: The Differences Explained

What is electro galvanizing?

Galvanneal vs Galvanized Steel: The Differences Explained 1

Electro galvanizing, commonly known as cold galvanizing, is an electrochemical process in which zinc ingots are used as anodes.

Zinc atoms lose electrons and become ions to dissolve in the electrolyte, while steel strips are used as cathodes.

Zinc ions get electrons on the steel strips to be reduced into zinc atoms and deposited on the surface of the steel strips to form a plating layer.

What is hot-dip galvanized sheet?

Galvanneal vs Galvanized Steel: The Differences Explained 2

There is a great difference in the amount of galvanizing between hot-dip galvanized sheet and electro galvanized sheet.

The galvanizing amount of hot-dip galvanizing cannot be too small.

Generally, the minimum is 50-60g/m2 on both sides, and the maximum is 600g/m2.

The galvanized layer of the electro galvanized sheet can be very thin, with a minimum of 15g/m2.

However, if the coating is required to be thick, the production line speed is very slow, which is not suitable for the process characteristics of modern units.

Generally, the maximum is about 100g/m2.

Because of this, the production of electro galvanized sheet is greatly limited.

Electro galvanized vs hot galvanized sheet

Galvanneal vs Galvanized Steel: The Differences Explained 3

Expert 1 opinion

There are fundamental differences between hot-dip galvanized sheet and electro galvanized sheet in the coating structure.

There is a slightly brittle compound layer between the pure zinc coating of hot-dip galvanized sheet and the steel strip substrate.

Most of the pure zinc coating forms zinc flowers when it crystallizes, and the coating is uniform without pores.

However, the zinc atoms of the electro galvanized layer are only deposited on the surface of the steel strip, and are attached to the surface of the steel strip by physical action.

There are many holes for air drying, which is very easy to cause pitting corrosion due to corrosive media.

Therefore, the hot-dip galvanized sheet is more corrosion resistant than the electro galvanized sheet.

The heat treatment processes of hot-dip galvanized and electro galvanized sheets are also completely different.

Generally, hot-dip galvanized sheets are made of cold-rolled sheets, which are annealed and hot-dip galvanized continuously on the galvanizing line.

The steel strip is heated and cooled in a short time, so the strength and plasticity are affected to a certain extent.

Its stamping performance is worse than that of cold-rolled sheets with the same cold-rolled sheets degreased and annealed on professional production lines.

Electro galvanized sheet is made of cold-rolled sheet, which basically guarantees the same processing performance as cold-rolled sheet, but its complex process flow also increases the production cost.

In short, the production cost of hot-dip galvanized sheet is lower and the application range is wider, which has also become the main variety of galvanized sheet market.

Expert 2 opinion

Electro galvanizing is to galvanize through electrode reaction, while hot galvanizing is to dip raw materials into a zinc pot for galvanizing, which is an inter metal reaction and a physical reaction.

During hot-dip galvanizing, the surface of the raw material is a layer of intermetallic compounds, followed by zinc, while the surface of electro galvanizing is zinc, without an intermediate layer.

The electro galvanized zinc layer is thin and the hot-dip galvanized zinc layer is thick.

Electrogalvanizing can not be produced in large quantities, and the output is low, while hot-dip galvanizing can be produced in large quantities, and the output is high.

The surface state and corrosion resistance of electroplating are better than that of hot-dip zinc.

Galvanizing is better than hot-dip galvanizing, so the price is also expensive.

The cost of galvanizing is high, so the price is high. When the price of zinc aluminum alloy for hot galvanizing is high, it is more than 4W / ton.

The anti-corrosion principle of electro galvanizing and hot-dip galvanizing is the same. But the two processes are different.

After galvanizing, the surface is smooth and bright. However, since the zinc layer is attached, it will fall off over time.

Hot dip galvanizing is not as beautiful as electroplating.

However, the zinc layer has penetration, and the service time is longer than that of electroplating.

Expert 3 opinion

1. Generally, the zinc layer of hot-dip galvanized sheet is thicker, about 10um or more, and has strong corrosion resistance, so it is a commonly used zinc plating process.

The electro galvanizing is very thin, about 3-5um. The hot-dip surface is rough and bright, and there are zinc flowers in serious cases.

The electroplating is smooth and dark (dirty).

Galvanized steel produced by electroplating method has good processability, but the coating is thin and the corrosion resistance is not as good as hot-dip galvanized steel sheet.

The cold galvanized sheet is electro galvanized, with a small amount of zinc.

It is only galvanized on the outer pipe wall (hot plating – both inside and outside).

It is only 10-50g/m2, and its corrosion resistance is much different from that of the hot galvanized sheet pipe.

2. There are many electroless galvanizing in chemical industry, which is suitable for small parts;

Hot dip galvanized sheet is generally used for power equipment and components, and is suitable for large parts and equipment.

Electro galvanizing, commonly known as cold galvanized sheet, is an electrochemical method, in which zinc ingot is used as the anode, zinc atoms lose electrons and become ions to dissolve into the electrolyte, while the steel strip is used as the cathode, and zinc ions get electrons on the steel strip to be reduced into zinc atoms and deposited on the surface of the steel strip to form a coating.

The hot-dip galvanizing plate is to first pickle the steel pipe.

In order to remove the iron oxide on the surface of the steel pipe, after pickling, it is cleaned in the tank of ammonium chloride or zinc chloride aqueous solution or mixed aqueous solution of ammonium chloride and zinc chloride, and then sent to the hot-dip galvanizing tank.

3. There is a great difference in the amount of galvanizing between hot-dip galvanized sheet and electro galvanized sheet.

The galvanizing amount of hot-dip galvanized sheet cannot be too small.

Generally, the minimum is 50-60g/m2 on both sides, and the maximum is 600g/m2.

The galvanized layer of the electro galvanized sheet can be very thin, with a minimum of 15g/m2, but if the coating is required to be thick, the production line speed is very slow, which is not suitable for the process characteristics of modern units.

Generally, the maximum is about 100g/m2.

Because of this, the production of electro galvanized sheet is greatly limited.

4. There are fundamental differences in coating structure between hot-dip galvanized sheet and electro galvanized sheet.

There is a slightly brittle compound layer between the pure zinc coating of hot-dip galvanized sheet and the steel strip substrate.

Most of the pure zinc coating forms zinc flowers when it crystallizes, and the coating is uniform without pores.

However, the zinc atoms of the electro galvanized layer are only deposited on the surface of the steel strip, and are attached to the surface of the steel strip by physical action.

There are many holes for air drying, which is very easy to cause pitting corrosion due to corrosive media.

Therefore, the hot-dip galvanized sheet is more corrosion-resistant than the electro galvanized sheet.

5. The heat treatment processes of hot-dip galvanized sheet and electro galvanized sheet are also completely different.

Hot-dip galvanized sheet is generally made of cold hard sheet, which is continuously annealed and hot-dip galvanized on the galvanizing line.

The steel strip is heated in a short time and then cooled, so the strength and plasticity are affected to a certain extent.

Its stamping performance is worse than that of cold-rolled sheet after degreasing and annealing on the same cold hard sheet in a professional production line.

Electro galvanized sheet is made of cold-rolled sheet, which basically guarantees the same processing performance as cold-rolled sheet, but its complex process flow also increases the production cost.

In short, the production cost of hot-dip galvanized sheet is lower, and the application range is wider.

It has also become the main variety of galvanized sheet market.

6. Hot dip galvanized sheet pipe is a kind of alloy layer produced by the reaction between molten metal and iron matrix, which combines the matrix and coating.

Hot dip galvanized sheet has the advantages of uniform coating, strong adhesion and long service life.

In order to ensure the quality, most of the regular galvanized pipe manufacturers do not use galvanizing (cold plating).

Only those small enterprises with small scale and obsolete equipment use electro galvanizing, and of course, their prices are relatively cheap.

The Ministry of construction has officially announced that the cold galvanized sheet pipes with backward technology will be eliminated, and it is not allowed to use the cold galvanized sheet pipes as water and gas pipes.

Generally, the galvanized sheet used now is hot-dip galvanized sheet, while the wire trunking used for electrical purposes is cold galvanized sheet, with certain color differences.

How to distinguish between hot galvanizing and cold galvanizing?

Galvanneal vs Galvanized Steel: The Differences Explained 4

First of all, the process is different:

Hot Dip Galvanizing

Hot dip galvanizing is to immerse the workpiece in the molten zinc solution for a certain time after degreasing, pickling, dipping and drying, and then bring it out.

Cold galvanizing

Cold galvanizing, also known as electro galvanizing, is the use of electrolytic equipment to put the workpiece into a solution containing zinc salt after degreasing and pickling, and connect the negative electrode of the electrolytic equipment;

Place a zinc plate on the opposite side of the workpiece and connect it to the positive electrode of the electrolytic equipment.

When the power is turned on and the current is moved from the positive electrode to the negative electrode, a layer of zinc will be deposited on the workpiece.

Appearance difference:

Zinc Electroplating

The appearance of electro galvanizing is relatively smooth and bright, and the plating layer using the color passivation process is also yellow green as the main color, showing seven colors.

The plating layer with white passivation process is cyan white or white is green light, and the plating layer with white passivation process is slightly colorful at a certain angle with sunlight.

The corners and edges of complex workpieces are easy to be “burnt” and become gray, and the zinc layer in this part is thick.

It is easy to form a dead angle of current at the internal corner to generate an under current gray area, where the zinc layer is thin.

The workpiece is free of zinc lump and caking.

Hot Dip Galvanizing

The appearance of hot-dip galvanizing is slightly rough and silvery white than that of electro galvanizing.

It is easy to produce process water marks and a few drops, especially at one end of the workpiece.

However, the zinc layer of hot-dip galvanizing is dozens of times thicker than that of electro galvanizing, and its corrosion resistance is dozens of times that of electro galvanizing.

Difference between galvanized finished products:

1. The inner and outer walls of hot-dip galvanized steel pipes are galvanized, while the outer walls of cold-dip galvanized steel pipes are galvanized only;

2. The cold coating is even and thin;

The hot-dip coating is thick and uneven.

3. The appearance of cold plating is bright, and the color of hot plating is dark.

4. The cold coating has poor corrosion resistance due to its thin thickness;

The hot-dip coating is tens of times thicker than the cold galvanized coating, and forms an infiltration layer with the base metal, which has good corrosion resistance.

5. The cold galvanized steel pipe looks brighter and smooth;

The appearance of hot-dip galvanizing is not as delicate and bright as that of cold-dip galvanizing.

The surface of hot-dip galvanized steel pipe seems to have some uneven bumps, and the surface is not bright and reflective.

Will galvanized steel pipes rust?

When the steel pipe is exposed to the air, it reacts with oxygen, or is eroded into oxide by oxygen in the water, it will rust.

The galvanized steel pipe is galvanized to form a layer of galvanized layer to isolate the air, so it is more corrosion-resistant and less prone to rust.

Will the galvanized pipe rust?

Generally speaking, galvanized steel pipes are not easy to rust, which does not mean that they will not rust.

It is just a matter of time. After a long time of use, galvanized pipes will still rust;

In addition, if the environment is humid, or if it is exposed to rain for a long time, the galvanized steel pipe will soon be oxidized and spotted, and then it will rust.

In addition, there are two types of galvanized steel pipes: hot galvanized pipe and cold galvanized pipe.

Relatively speaking, hot galvanized pipe is less likely to rust than cold galvanized pipe.

How long does the cold galvanized steel pipe not rust?

Galvanneal vs Galvanized Steel: The Differences Explained 5

The rusting time of galvanized pipes is mainly related to the galvanizing method, thickness of galvanized layer, galvanizing amount, service environment and other factors.

Generally, the rusting of cold galvanized pipes is relatively fast:

The galvanized amount of cold galvanized steel pipe is low, and this galvanized pipe is only galvanized on the outside, but not on the inside of the steel pipe.

The amount of zinc on one side is about 20g/m2, so it is easy to rust.

Generally, the cold galvanized steel pipe will start to rust about a year under the normal use environment;

If the thickness is relatively thick, the rusting time will be extended.

Those below 2.75mm can take 2-3 years, and those above 3.0mm can take 3-5 years.

How to remove rust from galvanized pipes?

If the galvanized pipe is rusty, it can be derusted by some methods.

The main derusting methods of the galvanized pipe are:

1. First, clean the steel surface with solvent to remove the organic matters on the surface.

2. Then use wire brush and other tools to remove rust, mainly to remove loose or inclined rust and welding slag with wire brush.

3. When the galvanized pipe is cleaned by pickling, the rust on it is almost cleaned.

Do galvanized steel pipes need to be painted with antirust paint?

After the steel pipe is galvanized, the surface is covered with a layer of zinc coating, which separates the steel pipe from the atmosphere, avoids the direct contact and corrosion of the atmosphere to the steel pipe, and is protected.

As for the coating of zinc on the steel pipe surface, due to its strong chemical activity, a thin and dense layer of zinc carbonate will be formed in the air at normal temperature to protect the zinc from being oxidized.

Therefore, the galvanized pipe, whether the zinc on the surface or the steel pipe itself, is protected from rust and does not need to be painted with antirust paint.

Only when the zinc coating is damaged (for example, when the steel pipe is welded and the coating at the joint is burned), the steel pipe is exposed to the air and loses the protection of the zinc coating, and then it needs to be repainted with antirust paint.

The galvanized layer of galvanized steel pipe has anti rust function, and the general installation method is to connect with threads.

Generally, it is not necessary to brush anti rust paint, unless unconventional process connection, such as welding, is used.

It is necessary to brush the part of the damaged galvanized layer with anti rust paint.

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