The hot-dip coating surface of seamless steel pipes will have crystallization patterns of the coating metal during solidification. This crystallization pattern is especially obvious for galvanized seamless pipes, showing the appearance of beautiful zinc crystals, thus becoming the appearance of hot-dip galvanized seamless pipes. This important feature is usually called “zinc flower”. When the galvanizing solution contains other metal impurities, zinc splatter occurs. The size and shape of zinc flowers depend on the type and amount of impurities contained in the galvanizing solution. Common impurities include lead, aluminum, antimony, bismuth, tin and other metals.

According to the size of the zinc flower diameter, it can be divided into the following three types:

1. Big Zinc Flower

The spangles with a diameter larger than 3mm that can be distinguished by the naked eye are called large spangles. Some people also call them normal spangles or natural spangles. The internationally recognized optimal size is 8~12mm.

2. Small zinc flower

Zinc flowers with a diameter of 1~2mm are called small zinc flowers. When the hot-dip galvanized seamless pipe comes out of the galvanizing pool and sprays water mist or zinc powder onto the unsolidified zinc layer, one water mist droplet and one zinc powder particle will form a crystallization center, causing zinc to bloom per unit area. As the quantity increases and becomes smaller, small zinc flowers that can be distinguished by the naked eye will form on the surface of galvanized seamless pipes. Traditionally, the products produced by this process are called small zinc flowers. Because this process often results in uneven zinc patterns, uneven surface color, and high production costs, this process is currently not widely used.

3. No zinc flowers

The zinc flowers on the pipe cannot be seen with the naked eye, which is called no zinc flowers, also known as zero zinc flowers. This is accomplished by controlling the chemical composition of the zinc liquid. When hot-dip galvanizing, only a certain amount of aluminum is added to the zinc liquid, without adding lead, antimony, or tin, to produce zinc-free products. This process does not increase equipment or production costs, and can achieve a uniform surface appearance. Therefore, this process has been widely promoted and applied around the world.

In nature, lead and zinc are symbiotic deposits. When pyrometallurgy is used, the density of liquid lead is higher in the lower part and the density of molten zinc is lower in the upper part, so they can be separated. However, the saturation concentration of lead in zinc liquid is 2%, so there is a large amount of lead in crude zinc. Hot-dip galvanizing has a history of more than 150 years. At that time, there was no modern refining technology, and only crude zinc was used for hot-dip galvanizing production. Because lead was mixed into the zinc liquid, zinc spatter would definitely appear on the hot-dip galvanized pipe. Therefore, for a long time, there has been a misconception that hot-dip galvanized seamless pipes must have zinc flowers. Without zinc flowers, it is not a hot-dip galvanized seamless pipe. In fact, from the perspective of long-term use, the performance of hot-dip galvanized seamless pipes without zinc flowers will be better.

Hot-dip pure zinc products, the code is GI.

The characteristics of hot-dip pure zinc products are beautiful surface, good corrosion resistance and good processability.

It is divided into two types, one is normal zinc flowers, and the other is no zinc flowers. Previous hot-dip galvanizing products always had some zinc splatter on the surface because the lead in the zinc liquid could not be extracted very pure. Therefore, our old concept is that hot-dip galvanizing has splatter. With the needs of the automobile industry, if hot-dip galvanized automobile sheets need to be painted, zinc spatter will have an impact on the painting. Later, by reducing the lead content in zinc ingots and zinc liquid to dozens of ppm, We can produce products with no or very little spangle. For some special purposes such as construction, if you still like large zinc flowers, we can obtain large and beautiful zinc flowers by adding elements such as lead or antimony to the zinc liquid.

Alloyed products, its code is GA.

The advantage of this product is that the paint adhesion on the coating surface is particularly good, the corrosion resistance after painting is also very good, and its weldability is also very good.

However, its surface appearance is gray, which is not suitable for bare use. We do not recommend using it without painting, because its coating contains 7-15% iron. If it is not painted, This part of the iron will produce a very light red rust. Although the red rust will not expand further in terms of corrosion resistance, the appearance is not very good.

Therefore, the main use of zinc-iron alloy is in coating applications, such as the outer panels of cars and the side panels of refrigerators. GA products can be directly used. For refrigerator processing, it can be directly powder-sprayed and adhered without pre-treatment. The sex is also very good.

Aluminum zinc products

It is characterized by excellent corrosion resistance and very beautiful surface appearance. Its zinc flowers look like beautiful fish scales. They are very beautiful and can be used naked.

Its corrosion resistance is 2-6 times that of our ordinary hot-dip galvanizing. Its high temperature resistance is also relatively good. It can be used at 300℃ without discoloration. If used for a short time, it also has better performance at 700℃. Excellent color retention and excellent heat reflection.

Therefore, a large number of these products are now used in the construction and home appliance industry.

Internal and external plastic-coated steel pipes for water supply have the following characteristics:

First, the inner surface of the internal and external plastic-coated steel pipe has a plastic coating, which can keep the inside of the pipe smooth, reduce the resistance to water flow, and increase the flow of water. In addition, because the water volume is relatively smooth, the water flow needs can be ensured. At the same time, no scaling will occur inside the pipeline during use, and bacteria will not breed, reducing water pollution.

Second, the outer surface of the internal and external plastic-coated steel pipes has a plastic coating, which can increase the adaptability of the plastic-coated steel pipes. The coating on the outer surface of the steel pipe improves the corrosion resistance, strong water resistance, high oxidation resistance, and good solvent resistance. In addition, the environmental impact on plastic-coated steel pipes can be reduced. Because pipes must be buried underground when supplying water, adding an outer coating can effectively extend the service life of the pipes.

What are the procedures for inspecting plastic-coated steel pipes:

The main inspection methods for plastic-coated steel pipes include appearance inspection, appearance inspection, pinhole test, bending test, flattening test, low temperature test, etc. Each inspection method has its own focus.

Appearance inspection is to inspect the appearance quality of coated steel pipes with the naked eye.

Thickness measurement is to measure the coating thickness at any four orthogonal points on the circumference on any two cross-sections.

The pinhole test refers to using an electric spark leak detector to check the steel pipe coating at the specified test voltage, and also to check whether there is any electric spark.

Bending tests are usually performed on a pipe bending machine or mold. It is worth noting that there is no filler in the pipe during the bending test, and the weld is located on the side of the main bending surface.

The flattening test is to place the specimen between two flat plates and gradually compress it on the pressure testing machine until the distance between the two flat plates is four-fifths of the outer diameter of the specimen. During flattening, the weld of the coated steel pipe is perpendicular to the direction of load application. .

The low-temperature experiment refers to placing the test piece in a low-temperature box, staying there for one hour, and then placing it in a normal temperature environment.

_{Oxidation means that when steel is heated, it is oxidized to form iron oxide scale due to the action of CO2, H2O, O2 in the furnace gas. Approximately 0.5%-3% of the steel is oxidized to form iron oxide scale every time it is heated ( That is, burning loss), which reduces the yield rate. At the same time, the accumulation of iron oxide scale on the furnace bottom will cause erosion of the refractory material and reduce the service life of the furnace. In addition, the thermal conductivity of iron oxide scale is much lower than that of metal, which affects the heating of steel billet.}

_{(1) Steel pipe temperature The oxidation of steel is not severe before the temperature reaches 800°C, and the change speed of the tube blank temperature is obviously accelerated when the temperature of the tube blank reaches above 800°C;}

_{(2) High temperature residence time The longer the tube blank stays in the high temperature zone, the more serious the oxidation and burning damage will be;}

_{(3) The richer the oxidizing atmosphere in the furnace gas, the more serious the oxidation and burning loss will be.}

_{The ratio of the influence of the above three is basically 6:3:1.}

_{High-pressure water descaling on the heat treatment line of galvanized steel pipes. During the heat processing process of steel, the surface of the steel parts will be oxidized to varying degrees depending on the heating temperature and the length of time, and oxide scales of different thicknesses will be formed. In order to improve the surface quality and dimensional accuracy of steel pipes, a high-pressure water descaling process is used to remove oxide scale during the hot rolling process of steel pipes.}

_{During the heat treatment and heating process, oxide scale will also be formed on the surface of the steel pipe. Adding a high-pressure water descaling process has the following advantages:}

_{(1) Like the rolling process, the high-pressure water descaling process can significantly improve the surface quality of the steel pipe;}

_{(2) After the steel pipe is descaled and the oxide scale is removed, the steel pipe is cooled evenly and heat exchange is accelerated during quenching, which can reduce the quenching deformation of the steel pipe and increase the cooling rate;}

_{(3) During the straightening process of the steel pipe after heat treatment, the steel pipe will produce a large friction force on the straightening roller and cause roller wear. If there is oxide scale on the surface of the steel pipe, the wear process will be accelerated, and descaling will Can reduce roller wear;}

_{(4) Non-destructive testing is required after heat treatment of steel pipes. If there is oxide scale on the surface, it will affect the flaw detection effect. In severe cases, flaw detection will be impossible. The descaling process can avoid this situation.}

1. After the surface pretreatment of the steel pipe in the patching part, primer should be applied within 8 hours. The primer should be even and no leakage should be allowed.

2. After the primer is dry, you can apply topcoat and wrap the glass cloth. If the weld is higher than 2mm, use topcoat and talcum powder to make a putty with suitable consistency. After the primer is dry, apply it on both sides of the weld. , and scraped into a transition surface. The connection between the glass cloth and the anti-corrosion layer of the pipe body shall not be less than 100mm.

3. For the anti-corrosion layer of epoxy coal tar anti-corrosion steel pipe with ordinary grade structure, the second top coat can be applied only after the first top coat has dried. The thickness of the anti-corrosion layer should be greater than or equal to 0.2mm.

4. The anti-corrosion layer of the reinforced epoxy coal pitch anti-corrosion steel pipe can be wrapped with glass cloth after the first coat of topcoat. The glass cloth should be tightened, the surface should be smooth, without wrinkles and bulges, and the width of the edge should be 30 to 40mm. After winding the glass cloth, apply the second topcoat. The amount of paint should be full, and all the mesh holes of the glass cloth should be filled with paint. After the second coat of topcoat has dried, the third coat of topcoat can be applied. The thickness of the anti-corrosion layer should be greater than or equal to 0.4mm.

5. The anti-corrosion layer of the extra-strength structure should be carried out according to the above-mentioned order of topcoat and one layer of glass cloth. The winding direction of the two layers of glass cloth should be opposite. After the third topcoat is dry, the fourth topcoat can be applied. The thickness of the anti-corrosion layer should be greater than or equal to 0.6mm.

mend injuries

1. For wounds where iron is not exposed, the damaged anti-corrosion layer should be removed first, and then topcoat and glass cloth should be applied according to the structure of the anti-corrosion layer of the pipe body. The overlap between the glass cloth and the anti-corrosion layer of the pipe body should not be less than 100mm.

2. For wounds exposed to iron, surface pretreatment should be carried out according to the requirements of repairing, and then the wounds should be repaired in the order required by the structure of the anti-corrosion layer of the pipe body.

3. Quality inspection

4. Appearance inspection: Visually inspect each patch and each patched area. The surface of the anti-corrosion layer should be smooth and free of wrinkles and bulges. The glass cloth mesh should be filled with topcoat.