Hot Dip Galvanizing- The Ultimate Guide (2022)

Steel is a valuable material widely used in the construction and engineering industries. Steel is durable, versatile, and inexpensive, but It is prone to corrosion, especially in outdoor environments.

Hot Dip Galvanizing- The Ultimate Guide (1)

People tried to develop solutions for long-term savings, and they began to coat steel by dipping it in molten zinc after cleaning it. They used ‘Galvanization’ to describe the administration of electric shocks in the 19th century.

We’re going to dig deep into ‘Galvanization,’ but feel free to jump to any section that interests you:

  • Chapter 1: What is galvanizing?
  • Chapter 2: How does galvanizing protect steel from rusting?
  • Chapter 3: What are the types of galvanizing?
  • Chapter 4: Why choose hot-dip galvanizing?
  • Chapter 5: Hot-dip galvanizing process
  • Chapter 6: How much does hot-dip galvanizing cost?
  • Chapter 7: 6 Tips Before Hot-dip Galvanizing
  • Chapter 8: Specification of Hot-dipped Galvanized Steel

What Is Galvanizing?

Galvanizing is also named Galvanization (sometimes called Galvanising or Galvanisation). It is a process applying a zinc coating to the surface of the metal.

Galvanizing can reduce maintenance costs, and it is one of the most effective, practical, and economical solutions for protecting metal from corrosion.

How does galvanizing protect steel from rusting?

Galvanizing protects products in 2 ways.

Galvanizing creates a zinc coating that shields the metal from the surrounding environment. The zinc coating can prevent water and other elements in the air from corroding the steel underneath.

Hot Dip Galvanizing- The Ultimate Guide (2)

Galvanizing also protects metal products through “galvanic corrosion.” Zinc coating has an affinity towards being the anode contacting with many other types of metals, so it slows the corrosion of the products or the cathode.

What are the types of Galvanizing?

There are mainly four different processes for companies to galvanize metal in common, Pre galvanizing, Hot-dip galvanizing (HDG), Cold galvanizing, and Electric galvanizing.

Pre galvanizing is also called mill galvanizing, it means the metal galvanized in sheet format before cutting and further processing. Pre galvanizing places emphasis on the time the metal galvanized, it is the only type that galvanized before fabrication.

Hot-dip galvanizing is the application of a zinc coating by dipping cleaned, prepared metal articles in molten zinc, by which process alloy layers may be formed between the primary metal and the outer pure zinc layer.

Cold galvanizing is an actual painting or spraying process that coats the surface of a metal with zinc-rich paints.

(Video) A Guide To Hot Dip Galvanizing (How it works)

Electric galvanizing is a process involving electroplating, running a current of electricity through a saline/zinc solution with a zinc anode and steel conductor.

Why people choose hot-dip galvanizing?

Hot-dip galvanizing has proved to be superior in many respects to other methods of the galvanizing due to the individual application process; The advantages are listed below:

Low cost

There are two main parts to the cost: initial cost and lifetime cost.

Hot-dip galvanizing is a highly mechanized manufacturing process, which needs less labor and time costs compared to the cold galvanizing paint.

Minima maintenance for a long lifetime makes hot dipped galvanized products cost less compared to the electro galvanized and pre-galvanized steel.

Complete protection

Hot-dip galvanizing is a process immersing metal products into a zinc bath after manufacturing, such as cutting, forging, and welding. So it generates sturdy, durable, and permanent coverage to every part, even inaccessible corners, that is much better than other methods of galvanizing.

Ease of inspection

Hot Dip Galvanizing- The Ultimate Guide (7)

For hot dipped galvanized products, there are two main aspects you should inspect after galvanizing, the smoothness and thickness of the zinc coating.

Quality of zinc layer is assessed readily by eye, and the thickness is easy to test with magnetic thickness gauges according to the ISO1461 and the requirement of clients. You can check the detailed standard of hot-dipped galvanized steel below.

Hot-dip galvanizing process

Here is a diagram describing the process.

Hot Dip Galvanizing- The Ultimate Guide (8)

You also can see the video below.

How much does hot-dip galvanizing cost?

The price of zinc plating is mainly affected by the following aspects

The place factories located

Prices vary significantly from country to country, take our products as an example. Although the price of galvanizing keeps rising, the price in China is about 400 to 500 US dollars per ton in 2020, which is still far lower than that of Occident.

The price of zinc

Zinc is the primary consumable in the galvanizing process, and its price directly affects the galvanizing price.

Shape and size of the steel

The costs are determined by the ease of handling through the galvanizing process, the easier, the cheaper.

Galvanized standard

The better the surface finish of the zinc layer, the thicker the coating, the higher the price.

6 Things You Need to Know Before Hot-dip Galvanizing.

Galvanizing Standard

Galvanizing standards are not the same in a different market, take the rule of pole hardware that some of our clients require as an example:

All the products are galvanized according to the standard BS 729 or ASTM A123.

(Video) Hot-Dip Galvanizing: Protecting Steel For Generations

In addition to BS 729 or ASTM A123, all galvanizing meets the conditions set out below.

  • Hot-dip galvanizing is applied to all products such as structural steel, structural and sheet steel fabrications, tube assemblies, bolts, nuts, screws, and other small articles processed in bulk, steel castings, steel forgings, steel stampings, iron castings, and similar products.
  • Hot-dip galvanizing is applied to products such as wire, sheet steel, or tubing, which will later be processed into finished articles.

Colour

Under some circumstances, the whole coating may consist of alloy layers and, in such cases, the appearance may be a dull grey.

Material

Mild steel, low alloy steel, and cast iron are metals particularly suitable for hot-dip galvanizing, but other ferrous metals may also be hot-dip galvanized. The fabricator ensures that the items to be galvanized consist of ore proper for galvanizing.

Internal Stresses

The fabricator ensures that internal stresses in the material, brought about by such treatments as extensive cold working, bending, welding, etc., are relieved as is necessary before submission for hot-dip galvanizing. These stresses could lead to embrittlement or intercrystalline cracking after galvanizing.

Pickling

Hot Dip Galvanizing- The Ultimate Guide (9)

Surface contaminants that cannot be removed by pickling, such as, oil, fat, tar, paint, welding slag and similar impurities, are removed before pickling.

Crevices and pin holes are avoided in welds as they trap pickling acid and lead to premature corrosion of the zinc coating.

Articles are not be galvanized if their design and shapes are such that the pickling solution cannot be removed with certainty or if adequate venting or drainage is not possible to ensure a safe and effective galvanizing dip. If it is necessary to bore drainage or vent holes in articles, the supplier must obtain the consent of the customer.

Hot Dip Galvanizing Bath

Hot Dip Galvanizing- The Ultimate Guide (10)

The zinc of the hot-dip galvanizing bath contains not less than 98.5 % of zinc (by mass), according to ISO 752. No zinc impurities or additives, which could have a deleterious effect on the durability of the zinc coating is acceptable.

Specification of Hot-dipped Galvanized Steel

Coating Finished Appearance

Hot Dip Galvanizing- The Ultimate Guide (11)

The galvanizing coating is smooth, continuous, uniform and free from anything detrimental to the stated use of the coated article. It is free from acid spots and flux stains and no scale or blister. The coating isn’t removable by normal handling or packing.

Shiny, dull grey or spangled surface appearance are generally acceptable. A sizeable wet storage stain (white rust) is unacceptable.

Coating Thickness

Hot Dip Galvanizing- The Ultimate Guide (12)

For one of our customers, the thickness of the galvanizing coating complies with the minimum average values given in the table below when tested following the requirements set out below:

Item Description

Minimum Zinc Mass Deposited (g/sq.mm)

Minimum Average Coating Thickness (um)*

(Video) Basics of Hot Dip Galvanising - Training Module B220

Steel Items, 5mm thick and over

Steel Items between 2mm and 5mm thick

Steel Items under 2mm thick

Threaded Steel Items

Iron Casting

610

460

335

305

610

85

65

47

43

85

Galvanizing coating thickness and zinc mass

  • the minimum average thickness figures given in this table is defined as the lowest of the individual average values for the number of samples under test.

Coating Uniformity

The uniformity is of the galvanizing coating such that the minimum proper thickness measurement on any test sample is not more than 7um below the minimum average figure specified for that article in the table above.

Hot Dip Galvanizing- The Ultimate Guide (13)

Coating Mass

(Video) Hot Dip Galvanizing- Dipping Process....... in action

The mass of the galvanizing coating per square meter of the surface area complies with the minimum values given by the customers when tested under the requirements.

Coating Mass Test

Frequently asked questions(FAQs)

What is hot dip galvanizing?

Hot-dip galvanizing is the application of a zinc coating by dipping cleaned, prepared metal products in molten zinc, by which process alloy layers may be formed between the basic metal and the outer pure zinc layer.

How many types of galvanizing?

There are mainly four different processes for companies to galvanize metal in common:
Pre galvanizing
Hot-dip galvanizing (HDG)
Cold galvanizing
Electric galvanizing.

How does hot-dip galvanizing protect steel from rusting?

Galvanizing protects products in 2 ways.
Galvanizing creates a zinc coating that shields the metal from the surrounding environment. The zinc coating can prevent water and other elements in the air from corroding the steel underneath.
Galvanizing also protects metal products through “galvanic corrosion.” Zinc coating has an affinity towards being the anode contacting with many other types of metals, so it slows the corrosion of the products or the cathode.

Why choose hot-dip galvanizing?

Hot-dip galvanizing has proved to be superior in many respects to other methods of the galvanizing due to the special application process:
Lower cost
Less maintenance
Longer lifetime
Quick process
Resource-efficient
Ease of inspection.

How much does hot-dip galvanizing cost?

The price of zinc plating is mainly affected by the following aspects:
The place factories located. Prices vary significantly from country to country, take our products as an example. Although the price of galvanizing keeps rising, the price in China is about 400 to 500 US dollars per ton in 2020, which is still far lower than that of Occident.
The price of zinc. Zinc is the primary consumable in the galvanizing process, and its price directly affects the galvanizing price.
Shape and size of the steel. The costs are determined by the ease of handling through the galvanizing process, the easier, the cheaper.
Galvanized standard. The better the surface finish of the zinc layer, the thicker the coating, the higher the price.

(Video) HOT DIP GALVANISING PROCESS

FAQs

What are the three steps in hot dipped steel galvanizing? ›

The hot-dip galvanizing process consists of three steps: surface preparation, galvanizing, and inspection.

What are the drawbacks of hot dip galvanization? ›

4.2 THE DISADVANTAGES OF HOT DIP GALVANIZING

Hot dip galvanizing can only be done in a galvanizing plant. Site application is not possible. The colour of the zinc coating can be changed only by painting. The dimensions of the component or structure are limited by the size of the zinc bath.

Which is better hot dipped or galvanized? ›

Hot dip galvanizing provides much better corrosion resistance than electro galvanization because the zinc coating is typically 5 to 10 times thicker. For outdoor or caustic applications where corrosion-resistance is required, hot dip galvanized cable is the clear choice.

How long does hot-dip galvanizing last? ›

A key benefit of using Hot Dip Galvanizing is its durability. Data shows that galvanizing can provide between 34 to 170 years of protection for steel. One of the main atmospheric pollutants that affect the performance of hot dip galvanizing is Sulphur Dioxide.

What is the temperature for hot-dip galvanizing? ›

The Hot-Dip Galvanizing Kettle

The freshly cleaned steel is submerged into a kettle of molten zinc at 830°-850° F.

What is the thickness of hot-dip galvanizing coating? ›

Thickness should be between 1.4 and 3.9 mils (35 and 100 µm) depending on the coating grade.

Is hot-dip galvanized rust proof? ›

The bond that forms between the steel and zinc when materials are hot-dip galvanized is self-healing. This means that, when the zinc coating comes into contact with water, it reacts by building up extra protection for itself. This protection increases its rust and corrosion resistance.

What is better zinc or hot-dipped galvanized? ›

A zinc plated product will be shiny and smooth. A hot dip galvanised product has the best protection against rust, even though it's a bit ugly.

Can you weld hot-dipped galvanized steel? ›

Galvanized steel is welded satisfactorily using the GMA process and pure carbon dioxide shielding gas which provides excellent weld penetration, but considerable weld spatter. The use of a spatter release compound may be worthwhile.

Can you Galvanise rusty steel? ›

When hot-dip galvanizing older steel which has been recycled from another project, the steel can sometimes be in poor condition or badly corroded. However, as long as the steel sections are structurally sound and fit for purpose, it is possible to refurbish and hot-dip galvanize.

How do you keep galvanized steel from rusting? ›

The most important step in preventing corrosion on galvanized steel is keeping it out of environments where it is exposed to substances with a pH below 6 or above 12. One side of this requirement is that it is important to keep galvanized steel out of acid rain.

Can you paint over galvanized steel? ›

Can you paint over galvanised steel? Hot Dip Galvanizing by itself is a long lasting, cost effective means of corrosion protection. However, galvanised steel can be painted for the following reasons: add colour for aesthetic, camouflage, or safety purposes.

At what temperature does galvanized steel become toxic? ›

Zinc toxicity can occur when an individual is exposed to and breathes the heated yellowish fumes produced from welding or heating galvanized steel. For hot-dipped galvanized steel the recommended maximum temperature is 392 F (200 C), before the metal presents a toxicity risk.

What is the zinc bath? ›

4 HOT DIP GALVANIZING. This is a process by which iron and steel can be treated to prevent rusting. It involves dipping an article into a molten bath of zinc which reacts with the iron and forms a coating.

What is the difference between galvanized and hot-dipped galvanized? ›

In brief, hot dip galvanizing is a type of galvanizing. The key difference between galvanized and hot dip galvanized is that galvanized materials have a smooth and sharp finishing, whereas hot sip galvanized structures have a rough finishing.

What is DFT in galvanizing? ›

Dry film thickness (DFT) is the thickness of a coating as measured above the substrate. This can consist of a single layer or multiple layers. DFT is measured for cured coatings (after the coating dries). The thickness of a coating depends on the application and type of process employed.

How many microns is hot-dip galvanizing? ›

Average coating mass minimum g/m²

Note: 1g/m2 coating mass = 0.14 μm coating thickness.

How do you convert GSM to microns? ›

I can Simplify the calculation method for converting gr/m2 to micron or micrometer. = 7.4/cm*cm*cm. 1 cm = 10000 micron or micrometer. = 7.4/cm*cm*10^4 µ.

How long will galvanized steel last outside? ›

The zinc coating of hot-dipped galvanized steel will last in the harshest soil is 35 to 50 years and in less corrosive soil 75 years or more. Although humidity affects corrosion, temperature itself has less of an impact. Galvanized zinc coatings respond well in extreme cold and hot temperatures.

What lasts longer galvanized or stainless steel? ›

Stainless steel lasts much longer than galvanized steel, so when the longevity of the building project is of importance, using stainless steel is recommended. Stainless steel is much stronger than plain steel hotdip galvanized.

Does Galvanising weaken steel? ›

DOES HOT-DIP GALVANIZING AFFECT STEEL STRENGTH? The tests carried out showed that hot dip galvanizing has no effect on the mechanical properties of standard grades of steel.

Can you mix zinc and galvanized steel? ›

There is no fear of galvanic corrosion when galvanized steel is in contact with other zinc coatings. Common examples include the use of mechanically galvanized bolts to connect high-strength HDG structural steel, and connections between metallized bridge girders and galvanized cross-braces.

How long will zinc screws last outside? ›

During this process, the molten zinc reacts with the surface of the steel to form a series of zinc/iron alloys. These alloy layers protect steel from corrosion for 30-40 years and more.

Is galvanized or zinc better for outdoors? ›

Zinc plating or electroplating is a process where zinc is applied by using a current of electricity. It is a thinner coating than hot-dip galvanizing making it unsuitable for outdoor applications. Its advantages are its brightness and uniform color making it more aesthetically appealing.

Do you have to grind galvanized steel before welding? ›

Galvanized steel is just normal steel coated with a thick layer of zinc. While this protective layer keeps it from corroding, it also protects the steel quite well from being welded. If you're planning on MIG or TIG welding, you're almost always going to need to grind off the galvanized layer where you're welding.

Can you grind off galvanized coating? ›

The most common and preferred removal method is grinding back the zinc coating, but burning the zinc away or pushing it back from the weld area are also effective. Welding galvanized steel should always be done in well-ventilated locations to minimize fume inhalation.

What welding rod is best for galvanized steel? ›

6011 Electrode. The 6011 electrodes are known for burning through anything in their path. This is precisely the reason why they're good for welding galvanized steel and are considered some of the best all-purpose welding rods.

What is the process of hot-dip galvanizing? ›

The hot dip galvanizing process is relatively simple. It involves cleaning steel and immersing it in molten zinc to obtain a coating. Hot dip galvanizing is the process of coating iron or steel with a layer of zinc by immersing the metal in a bath of molten zinc at a temperature of around 450 °C (842 °F).

What is the process of galvanising steel? ›

Prepared items are galvanized by immersion in molten zinc. On immersion in the galvanizing bath the steel surface is completely covered by the molten zinc, which reacts with the steel to form a series of zinc-iron alloy layers.

What is the process of galvanising? ›

Galvanisation or galvanization (or galvanizing as it is most commonly called) is the process of applying a protective zinc coating to iron or steel, to prevent rusting. The most common method is hot dip galvanizing, in which steel sections are submerged in a bath of molten zinc.

Is the first step of galvanizing process? ›

Galvanizing steel consists of just three steps: Surface Preparation.
...
Surface Preparation
  • Degreasing/Caustic Cleaning. An acidic “bath” removes organic contaminants from the steel surface. ...
  • Picking. A dilute solution of acid is used to remove mill scale and rust from the steel. ...
  • Fluxing.
22 Aug 2016

Can you Galvanise over galvanised? ›

Material with zinc or traces of zinc on it, for example because it has been galvanised previously, can only be galvanised again if the old zinc coating has been removed entirely.

Can hot-dipped galvanized steel be painted? ›

Hot Dip Galvanizing by itself is a long lasting, cost effective means of corrosion protection. However, galvanised steel can be painted for the following reasons: add colour for aesthetic, camouflage, or safety purposes.

What temperature does galvanized steel become toxic? ›

Zinc toxicity can occur when an individual is exposed to and breathes the heated yellowish fumes produced from welding or heating galvanized steel. For hot-dipped galvanized steel the recommended maximum temperature is 392 F (200 C), before the metal presents a toxicity risk.

How many types of galvanizing are there? ›

There are two main methods for galvanizing steel; these are hot-dip galvanizing and cold galvanizing.

What is the difference between galvanized and hot dipped galvanized? ›

In brief, hot dip galvanizing is a type of galvanizing. The key difference between galvanized and hot dip galvanized is that galvanized materials have a smooth and sharp finishing, whereas hot sip galvanized structures have a rough finishing.

What chemicals are used in galvanising? ›

Zinc ammonium chloride fluxes are used for all types of galvanizing - after-fabrication galvanizing as well as continuous sheet, wire, and tube galvanizing operations. As flux is a relatively low melting temperature inorganic chemical, the steel sheet cannot be heated to high temperatures ahead of the galvanizing bath.

How long does it take for galvanized steel to rust? ›

The zinc coating of hot-dipped galvanized steel will last in the harshest soil is 35 to 50 years and in less corrosive soil 75 years or more. Although humidity affects corrosion, temperature itself has less of an impact.

Is galvanized better than stainless steel? ›

Stainless steel is almost always more robust than galvanized steel. So if structural elements are involved, stainless will likely be a better bet. Stainless steel provides stronger corrosion resistance than galvanized steel -- especially in marine environments.

How long does it take to galvanize steel? ›

Galvanizing leadtimes can vary depending on the time of year and how much demand there is within the industry, however most orders are completed within one week. The actual process of Hot Dip Galvanizing takes approximately half a day from start to finish so small urgent items are often processed within 24 – 48 hours.

Why zinc is used in galvanisation? ›

The reason that the galvanizing process uses zinc instead of other metals is that zinc oxidizes and experiences acid corrosion “sacrificially” to steel. That means that when zinc is in contact with steel, oxygen and acids will attack the zinc rather than the steel beneath it.

Which metal is used in galvanisation? ›

Answer : Zinc metal is used for galvanising iron because it is more reactive than iron. It reacts with air to form a hard layer of zinc oxide, which prevents air and moisture to come in contact with iron. Q.

Is galvanized rust proof? ›

Galvanized steel takes a long time to rust, but it will eventually rust. This type is carbon steel that has been galvanized or coated with a thin layer of zinc. The zinc acts as a barrier preventing oxygen and water from reaching the steel, providing advanced corrosion protection.

Videos

1. Hot Dip Galvanising Methods
(METaL)
2. Hot-Dip Galvanizing Process
(American Galvanizers Association)
3. All About Hot Dip Galvanized Fasteners | Fasteners 101
(Albany County Fasteners)
4. Design For Hot Dip Galvanizing - Sperrin Galvanisers
(Sperrin Galvanisers)
5. High-Efficiency Hot Dip Galvanizing Plant Designed by Western Technologies.
(Western Technologies, Inc.)
6. Hot-Dip Galvanized Steel Coating Appearance: Process Marks & Inclusions
(American Galvanizers Association)

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