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Hot Dip Galvanized Pipe

Hot dipped galvanized steel pipe is in manufacturing process using steel pipes of removed rust dipped into zinc liquid of 500℃ temperatures, and making steel surface attached zinc layer so as to achieve the purpose of anti-corrosion.

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Description

Hot dipped galvanized steel pipe is in manufacturing process using steel pipes of removed rust dipped into zinc liquid of 500℃ temperatures, and making steel surface attached zinc layer so as to achieve the purpose of anti-corrosion.

Hot-dip galvanizing (HDG) is the process of coating iron, steel or ferrous materials with a layer of zinc. This done by passing the metal through molten zinc at a temperature of 860°F (460°C) to form zinc carbonate (ZNC03). Zinc carbonate is a strong material that protects steel and can prevent corrosion in many circumstances. Hot-dip galvanizing can be carried out cheaply and in large batches.

Hot dipped galvanized with PE coating welded steel pipes

Galvanizing is one of the most widely used to methods for protecting metal from corrosion. It involves applying a thin coating of zinc to a thicker base metal, helping to shield it from the surrounding environment. The next time you are in your car, take a look at the street signs and lamp posts you pass. A large number of them will have a mute, silver color on them. That “silver” is actually the coating of zinc.

Thus, PE Coated Steel Pipes have been highly acclaimed even under severe environments such as areas of extreme cold, desert regions and under the sea.

Hot-dip galvanizing involves three main steps

Preparation: The galvanizing reaction will only occur on a chemically clean surface, so the first step of the process involves removing contamination. First, the metal is degreased using a caustic solution and then dipped in hydrochloric acid to remove rust, mill scale, welding slag, paint and grease. This followed by a rinse and a dip in a flux solution, which is usually about 30 percent zinc ammonium chloride.

Galvanizing: When the clean iron or steel component is dipped into the molten zinc (at 842°F (450°C)), zinc-iron alloy layers form as a result of a metallurgical reaction between the iron and zinc. When the material is pulled from the galvanizing bath, a layer of molten zinc is present on top of the alloy layer. When it cools, it has the bright, shiny appearance associated with galvanized products.

Inspection: After galvanizing, the coated materials are inspected for coating thickness and coating appearance. A variety of simple physical and laboratory tests may be performed to determine thickness, uniformity, adherence and appearance of the zinc coating.

Quite simply, galvanizing a metal gives it anti-corrosion properties. Without the protective zinc coating, the metal would remain exposed to the elements and potentially oxidize and corrode much faster. Galvanized Steel is a cost effective alternative to using materials such as austenitic stainless steel or aluminum in order to prevent corrosion.

How Does It Work?

Galvanizing can protect metal is a number of ways. Firstly, it creates a protective coating that shields the metal from the surrounding environment. The layer of zinc prevents water and moisture and other elements in the air from corroding the steel underneath. Should the zinc coating be scratched deep enough, the metal would become exposed and susceptible to corrosion.

raw material pre galvanized steel strip

Galvanizing can also protect metal through a process called “galvanic corrosion”. Galvanic corrosion occurs when two metals of a different electrochemical make up are placed into contact with one another with an electrolyte present, such as salty water. Depending on the atomic structure of the two metals, one metal is the anode and the other is the cathode. The anode corrodes more rapidly than it would by itself and the cathode corrodes at a slower pace than it would by itself. The reason zinc is used for galvanizing is because it has an affinity towards being the anode when in contact with many different types of metals. Since the zinc coating in contact with the base metal is usually the anode, it slows the corrosion of the base metal, or the cathode.

The difference between hot dip galvanizing and cold galvanizing

1. Essential difference

Cold galvanizing, also known as electro-galvanizing, is to use electrolytic equipment to deoil and pickle the workpiece into a solution of acid salt, and connect the negative electrode of the point solution equipment, and place a zinc plate on the opposite side of the workpiece to connect to the electrolytic equipment. The positive electrode, turn on the power supply, and use the current to move from the positive electrode to the negative electrode, which will deposit a layer of zinc on the workpiece.

Hot-dip galvanizing (galvanized steel tube) is also called hot-dip galvanizing. It is a method of immersing steel hooks in molten zinc to obtain a metal coating, you can bring it up.

2. Principle difference

Cold galvanizing uses chemical principles to separate zinc alloys into zinc ions, which are attached to the surface of steel. Generally, the zinc layer is thin, and steel is easily corroded in general environments. Generally, cold galvanizing is used for anti-corrosion of various steel products and structures. The amount of galvanizing of cold galvanizing is very small, only 10-50g per square meter.

As we all know, the mechanism of zinc’s resistance to atmospheric corrosion includes mechanical protection and electrochemical protection. Under atmospheric corrosion conditions, the surface of the zinc layer has ZnO, Zn(OH)2 and basic zinc carbonate protective films, which slow down the corrosion of zinc to a certain extent. The protective film (also known as white rust) is damaged and a new layer is formed. When the zinc layer is seriously damaged and endangers the iron matrix, zinc produces electrochemical protection for the matrix. The standard potential of zinc is -0.76V, and the standard potential of iron is -0.44V. When zinc and iron form a microbattery, zinc is dissolved as an anode. , the iron is protected as a cathode. The formation process of the hot-dip galvanized layer is the process of forming an iron-zinc alloy between the iron matrix and the outer pure zinc layer. The iron-zinc alloy layer is formed on the surface of the workpiece during hot-dip plating, which can make the iron and pure zinc layer very close. good combination.

3. Appearance difference

Hot-dip galvanized looks rougher in appearance, while cold-dip galvanized is brighter and smoother.

The appearance of hot-dip galvanizing is not as delicate and bright as cold galvanizing, but the thickness of the zinc layer is dozens of times that of cold galvanizing. The anti-corrosion performance is that the electroplating hot-dip galvanized layer is thick, and the surface of the coating generally has sequins that can be recognized by the naked eye, and the surface can be touched by hand. It feels a certain roughness and has a bright silver appearance. When the temperature of hot-dip galvanizing production is too high, the appearance is mainly gray, and the small pieces of the zinc-iron alloy layer will fall off when knocked.

Cold galvanized steel pipe introduction

Cold galvanized steel pipe is using electric chemical processing coated zinc layer on steel  pipe. The zinc layer usually 20~30μm thick.

Manufacturing process of cold galvanized steel pipe:

Degreasing – electroplating – passivation – drying – packaging

Zinc thickness for cold galvanized steel pipe

Cold galvanized steel pipe zinc thickness is 5-15 μm, the layer is dense, and there is no inclusion with organic matter.

Cold galvanization technology is no longer recommend for pipe products.

For more thinner zinc layer reason, countries of the world have gradually forbidding the cold galvanized steel pipe as water pipe and coal gas pipe. But due to cold galvanizing processing have smooth appearance of surface, it always used in manufacturing small pieces which requiring precise plating. Such as screws, Machinery manufacturing, electronics, precision instruments, chemicals, light industry, transportation, weapons, aerospace, atomic energy, etc., in the national economy has great significance.

What’s the difference between Pre – galvanized and Hot- galvanized steel pipe?

Galvanized steel pipes: one is pregalvanized steel pipe, short for GI pipe; The other is hot dipped galvanized steel pipe. For hot dipped galvanized steel pipe, it includes two technologies: galvanized by zinc blowing machine and galvanized by zinc pool.

Hot dip galvanizing pipe is that a Pipe was dipped into the bath after fabrication.Thickness by this method will reach minimum up to 45 µm and the thickness of the zinc coating is influenced by a number of factors, including the surface of the steel, the time the steel is dipped in the bath, the composition of the steel as well as the steel’s size and thickness.

One advantage of hot dip galvanizing is that the entire part is covered including the edges, welds, etc. giving it an all-round corrosion protection. The end product can be used outdoors in all different weather conditions. It is the most popular galvanizing method and is widely used in the construction industry.

Pre-galvanizing pipe, also known as mill galvanized pipe, hot dip mill galvanized or continuous hot dip galvanized.Pre-galvanized steel pipe refers to pipe which was galvanized while in sheet format, thus prior to further manufacturing. After the sheet is sent through the mill to be galvanized it is cut to size and recoiled.the pipe thickness will be minimum 12 µm.

One of the advantages which pre-galvanized steel has over hot dip galvanized steel is that it has a better appearance.pre-galvanized materials are used for a wide variety of products including conduit, lip and open channels.

How to distinguish the hot-dip galvanized steel pipe and electro galvanized steel pipe?

hot dip galvanizing vs electro galvanizing

Galvanized pipes are the pipes that a layer of protective zinc coating to pipe in order to prevent premature rust and corrosion. There are several different processes for galvanizing steel pipe,Hot-Dip Galvanizing and Electrogalvanizing are the most commonly used ways for steel pipes.To distinguish the Galvanized steel pipe and Electrogalvanized steel pipe,you should understand the manufacturing process of them.

Hot-Dip Galvanizing

As the name implies, this method involves dipping the base metal into a molten pool of zinc. First, the base metal must be cleaned either mechanically, chemically, or both to assure a quality bond can be made between the base metal and the zinc coating. Once cleaned, the base metal is then fluxed to rid it of any residual oxides that might remain after the cleaning process. The base metal is then dipped into a liquid bath of heated zinc and a metallurgical bond is formed.

Electro-galvanizing

Electrogralvanizing utilizes an electrical current in an electrolyte solution to transfer zinc ions onto the base metal. This involves electrically reducing positively charged zinc ions to zinc metal which are then deposited on the positively charged material. Grain refiners can also be added which helps to ensure a smooth zinc coating on the steel.

The main difference between Galvanized pipes and Electrogalvanized steel pipe

1.The zinc layer

The thickness of hot dip galvanized zinc layer can achieved more than 50 microns, the maximum can reach 100 microns.Electro-galvanized zinc layer generally in the 3 to 5 microns, special requirements can also reach 7 to 8 microns.

2.Appearance

hot dip galvanization has dull, unpleasant finish.However, Electro-galvanization comes with excellent finish.

3.Life

Hot dip galvanized pipe is known to have very high life averaging between 20 to 50 years. But, lectro-galvanization has very low life, ranging from several months to some years only.

4.Costs

The cost is said to increase proportionately with higher coating thickness. hence the hot dip galvanized pipe with normal coat thickness about 40% expensive than electro-galvanizing pipe.

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