Characteristics Of Conventional Zinc Coating Of Galvanized Products

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Hot-dip pure zinc products, 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 spangles, and the other is zinc-free spangles. In the past, hot-dip galvanized products always had some zinc spangles on the surface because the lead in the zinc liquid could not be refined very pure, so our old concept is that hot-dip galvanizing has zinc spangles. With the needs of the automotive industry, if hot-dip galvanized automotive plates are to be painted, zinc spangles 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 zinc spangles. For some special uses such as buildings, if you still like large zinc spangles, we can add elements such as lead or antimony to the zinc liquid to obtain large and beautiful zinc spangles.

Alloyed products, its code is GA.

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

But its surface morphology is gray, which is not suitable for bare use. We do not recommend it if it is not painted, because its coating contains 7-15% iron. If it is not painted, this part of iron will generate 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 still in the use occasions with painting, just like the outer panel of the car and the side panel of the refrigerator. GA products can be directly used. For refrigerator processing, it can be directly powder-sprayed without pre-treatment, and the adhesion is also very good.

Aluminum-zinc products

The characteristics are particularly good corrosion resistance and beautiful surface appearance. Its zinc flowers look like beautiful fish scales, very beautiful, and can be used directly bare.

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 a better color retention ability at 700℃, and has excellent heat reflection effect.

Therefore, this kind of product is now widely used in the construction and home appliance industries.

Application Scope Of 3PE Anti-corrosion Steel ipe For Drinking Water

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The function of the pipeline is mainly to transport liquids or other solids. It can be said to be the most commonly used equipment in our lives. 3 treatment methods for pipeline anti-corrosion.

1. What are the treatment methods for pipeline anti-corrosion?

1. Pipeline external anti-corrosion design Petroleum asphalt is the oldest pipeline anti-corrosion layer, which is well used in most dry areas. At present, epoxy coal tar, zinc-rich coatings, etc. have replaced petroleum asphalt as anti-corrosion coatings for steel water pipelines, and epoxy coal tar series coatings have excellent anti-corrosion performance and low prices.

2. The anti-corrosion coating on the outer wall of the pipeline is evenly and densely applied on the surface of the rust-removed metal pipeline to isolate it from various corrosive media. It is one of the most basic methods for pipeline anti-corrosion. Since the 1970s, laying pipelines in harsh environments such as polar regions and oceans, and heating and transporting oil products to increase the temperature of the pipeline, have put forward more requirements on the performance of the coating.

3. Pipeline inner wall anti-corrosion coating Surface treatment of the inner wall of the pipe can ensure that the coating is firmly bonded to the pipe wall. Since the 1970s, the trend has been to use the same material for the inner and outer wall coatings of the pipe so that the inner and outer wall coatings can be carried out simultaneously. Before the pipeline is treated for corrosion, the surface of the pipeline substrate must be treated to remove moisture, oil, dirt, pollutants, rust and scale on the surface of the substrate. There are many methods for surface treatment, and manual rust removal, sandblasting or chemical rust removal are generally used. When removing rust manually, the quality standard should reach St3 level; when sandblasting or chemical rust removal, the quality standard should reach Sa2.5 level, and the surface roughness of 30 to 50µm is more appropriate. The treated surface should be primed within 4 hours.

2. What is the role of pipeline anti-corrosion?

1. Prevent the pipeline from being corroded by soil, air, medium, etc. Nowadays, pipelines are mostly used to transport gasoline, natural gas and other substances. These substances have a very large corrosive effect on the soil of the environment, and pipelines can effectively prevent the environment from being polluted by these substances, and greatly improve the transportation efficiency.

2. Pipeline anti-corrosion can prevent the leakage of natural gas, oil, etc., and has a very good protection and prevention effect on fire and the environment.

3. What are the precautions during pipeline anti-corrosion construction?

1. The ambient temperature should be higher than 5℃ and the air humidity should be lower than 80% during the construction of the anti-corrosion layer.

2. The diluent ratio is 5%, the glass cloth is pressed 20-25mm, and the overlap length of the cloth head is 100-150mm.

3. Anti-corrosion layer voltage inspection: ordinary level 2000V; reinforced level 2500V; extra reinforced level 3000V.

4. Anti-corrosion layer inspection: every 10km leakage point ≯5, use a low-voltage audio signal leak detector to measure.

Hot-dip Galvanized Steel Pipe Welding Construction Process

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Before hot-dip galvanized steel pipe welding, the hot-dip galvanized steel pipe is mainly heated, and welding begins after temperature control for 30 minutes. The heating, solid layer temperature and heat treatment process of welding are automatically controlled by the temperature control cabinet of the heat treatment process. The far-infrared crawler heat treatment furnace is used to automatically set the curve and describe the curve, and the thermal resistor measures the temperature.

During heating, the distance between the thermal resistance measurement points is 15mm-20mm from the weld boundary. In order to better prevent the hot-dip galvanized steel pipe from welding deformation, each column joint is welded symmetrically by two people, and the welding direction is from the middle to both sides.

When welding the inner opening, the first to the third layer must be operated in small specifications, because its welding is the primary cause of welding deformation.

After welding one to three layers, clean the reverse side. After removing the root with carbon arc air gouging, the weld needs to be mechanically polished and polished, and the weld surface needs to be combed for nitriding treatment to expose the metal texture to prevent the surface from being optimistically carbonized and cracked. The outer mouth needs to be welded once, and there will be some residual material in the inner mouth. When welding the second layer of hot-dip galvanized steel pipe, the welding direction should be opposite to that of the layer, and so on. Each layer of welding joints should be spaced 15-20mm apart.

When welding hot-dip galvanized steel pipes, the welding current, welding speed and number of welding stacks of the two welders should be consistent. When welding, the welding should start from the arc starting plate and end on the arc starting end plate. Cut off and grind and polish after welding.

Post-weld heat treatment: The heat treatment process should be carried out within 12 hours after the weld is welded. If the heat treatment process cannot be carried out immediately, insulation, slow cooling and other methods should be used. After the quenching and tempering treatment is completed, two thermal resistors should be used to measure the temperature, and the thermal resistors should be welded on both sides of the weld. According to the “Standards for Construction and Inspection of Steel Structure Engineering”, the welds are inspected by ultrasonic flaw detectors, and the inspection market share is 100%.

Pressure Resistance And Insulation Function Of Plastic-coated Steel Pipe

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The buried pipeline uses plastic-coated steel pipe for the transmission line tower, which is composed of towers connected by tower pole devices. The pole tower is made of steel. The surface of the tower pole steel and the inner and outer surfaces of the tower pole are hot-dipped with a modified polyethylene plastic layer. The plastic-coated steel pipe is a steel pipe coated with red modified epoxy resin powder inside and outside. It is a new type of steel pipe made on the basis of steel pipe, through sandblasting chemical pretreatment, preheating, inner and outer coating, curing, post-treatment and other processes.

It successfully solves the problems of burial, rust, scaling and other problems of plastic-coated steel pipe. There will be no pipe blocking and spray blocking, which improves the service life of fire water supply pipelines. The plastic-coated steel pipe mainly focuses on the excellent mechanical properties of steel and the excellent chemical corrosion resistance of polymer materials. The product has excellent anti-static, high-pressure and flame-retardant properties, and can withstand harsh use environments. Its super corrosion resistance greatly improves the service life of the pipeline.

This steel pipe has good pressure resistance and thermal insulation properties. It mainly protects the wires, so leakage will not occur at all. So far, plastic-coated steel pipe manufacturers are changing these advantages. The pipe wall is relatively smooth and burr-free. It is suitable for crossing cables or wires during construction.

Fire buried pipe plastic-coated steel pipe has the advantages of smooth wall thickness, good drainage performance, low fluid resistance, and no scaling, which can greatly reduce losses compared with other pipes. At the same time, the linear expansion coefficient of large-diameter plastic-coated pipes is very small, making it very advantageous as a main pipeline, greatly overcoming the defects of other plastic pipes and ordinary pipes with large linear expansion coefficients.

Plastic-coated steel pipe is an upgraded product of traditional steel-plastic pipes and galvanized pipes. It has comprehensive properties such as high strength, high elongation, good low-temperature brittleness, low expansion coefficient, corrosion resistance, wear resistance, and low fluid resistance. It belongs to a new type of water supply and drainage, anti-corrosion green large-diameter pipeline, which is more and more widely used in domestic industry.

Ten Key Points Of Heat Treatment Of Galvanized Pipes

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1. Galvanized pipes and fixtures should be cleaned of foreign objects such as oil, residual salt, paint, etc. before heat treatment;

2. The fixtures used in the vacuum furnace for the first time should be degassed and purified in advance at a vacuum degree not lower than the required degree of the workpiece;

3. Workpieces that are easy to deform during the heat treatment process should be heated on special fixtures. The preheating methods are: one preheating is 800℃, the second preheating is 500-550℃ and 850℃, and the temperature rise rate of the first preheating should be limited;

4. Workpieces with complex shapes or sharp changes in cross-section and large effective thickness should be preheated;

5. Workpieces with grooves and no through holes, castings and welded parts, and stainless steel workpieces that have been processed and formed are generally not suitable for heating in salt bath furnaces;

6. According to the effective thickness and conditional thickness of the workpiece (actual thickness multiplied by the workpiece shape coefficient), the galvanized pipe should have sufficient insulation time for heating;

7. Galvanizing of martensitic stainless steel and heat-resistant steel The pipe can be cleaned, cryogenically treated or tempered only after quenching and cooling to room temperature. The time interval between welding and subsequent heat treatment should not exceed 4 hours;

8. According to the requirements and surface conditions of the galvanized pipe, alkali washing, water-soluble cleaning agent, chlorine solvent sandblasting, shot blasting and other methods should be used for cleaning;

9. After correction, stress relief annealing should be carried out at a temperature lower than the original tempering temperature. For workpieces with complex shapes or strict size requirements, correction should be carried out with a shaping fixture combined with tempering during tempering after correction;

10. When the mechanical properties of the galvanized pipe are unqualified, repeated heat treatment can be carried out, but the number of repeated quenching or solid solution is generally not more than two times. Supplementary tempering of galvanized pipes is not counted as repeated treatment. Martensitic stainless steel and heat-resistant steel workpieces in the quenched state or after low-temperature tempering should be preheated, annealed or high-temperature tempered before repeated quenching.

To improve the quality of galvanized pipes, it is necessary to reduce zinc slag to reduce the iron content in the zinc liquid, that is, to start with the factors that reduce iron dissolution. Only in this way can a high-quality galvanized layer be formed on the surface of our galvanized square pipes.

Pressure Resistance And Insulation Function Of Plastic-coated Steel Pipe

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The transmission line tower of the buried pipeline adopts plastic-coated steel pipe, which is composed of towers connected by tower pole devices. The pole tower is made of steel. The surface of the tower pole steel and the inner and outer surfaces of the tower pole are hot-dipped with modified polyethylene plastic layer. The plastic-coated steel pipe is a steel pipe coated with red modified epoxy resin powder inside and outside. It is a new type of steel pipe made of steel pipe through sandblasting chemical pretreatment, preheating, inner and outer coating, curing, post-treatment and other processes.

It successfully solves the problems of burial, rust and scaling of plastic-coated steel pipe. There will be no pipe blocking and spray blocking, which improves the service life of fire water supply pipelines. Plastic-coated steel pipes mainly focus on the excellent mechanical properties of steel and the excellent chemical corrosion resistance of polymer materials. The product has excellent anti-static, high-pressure and flame-retardant properties, and can withstand harsh use environments. Its super corrosion resistance greatly improves the service life of the pipeline.

This steel pipe has good pressure resistance and thermal insulation performance. It mainly protects the wires, so leakage will not occur at all. So far, plastic-coated steel pipe manufacturers are changing these advantages. The pipe wall is relatively smooth and burr-free. It is suitable for crossing cables or wires during construction.

Fire-fighting buried pipe plastic-coated steel pipe has the advantages of smooth wall thickness, good drainage performance, low fluid resistance, and no scaling, which can greatly reduce losses compared with other pipes. At the same time, the linear expansion coefficient of large-diameter plastic-coated pipes is very small, making it very advantageous as a main pipeline, greatly overcoming the defects of other plastic pipes and ordinary pipes with large linear expansion coefficients.

Plastic-coated steel pipe is an upgraded product of traditional steel-plastic pipes and galvanized pipes. It has comprehensive properties such as high strength, high elongation, good low-temperature brittleness, low expansion coefficient, corrosion resistance, wear resistance, and low fluid resistance. It belongs to a new type of water supply and drainage, anti-corrosion green large-diameter pipeline, which is more and more widely used in domestic industry.

Application of plastic-coated steel pipes

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Plastic-coated steel pipes are used everywhere in life, such as building water supply pipes, fire water supply pipes, special pipes for coal mines, hot spring anti-corrosion and thermal insulation pipes, and cable protection pipes commonly seen in modern life. Common steel-plastic composite pipes are actually mainly plastic-lined steel pipes and plastic-coated steel pipes. The following is an explanation of the application of plastic-coated steel pipes.

According to the different internal and external coating materials, they can be divided into epoxy resin coated steel pipes and polyethylene coated steel pipes. Both are based on welded steel pipes and seamless steel pipes. They are green and environmentally friendly pipes that are corrosion-resistant, erosion-resistant, non-toxic, and radiation-free.

Corrosion of steel is very common, and the economic losses caused by it are huge. Plastic-coated steel pipes retain the rigidity and strength of traditional metal pipes due to the coating of the inner and outer walls. The rigidity and strength are far superior to plastic pipes and aluminum-plastic pipes; at the same time, because the inner wall is also sprayed, the pipe has the characteristics of smooth inner wall, small friction resistance and no scaling, and the outer wall is more beautiful. The good qualities of these pipes have won inherent advantages for their wide application.

Furthermore, the connection method between pipes is the most important issue in the building materials industry. Whether the connection strength is reliable, whether it is convenient to install and maintain, and whether it can adapt to harsh natural conditions are the most concerned issues for each unit. The current plastic-coated steel pipe manufacturers are very humane. From the perspective of customers, design, construction and other units, the connection method, steel pipe length and color can be specified.

Plastic-coated steel pipes are used for various fluid transportation and have excellent corrosion resistance and relatively small friction resistance. Epoxy resin coated steel pipes are suitable for the transportation of water supply and drainage, seawater, warm water, oil, gas and other media, and polyvinyl chloride coated steel pipes are suitable for the transportation of drainage, seawater, oil, gas and other media. It is used in various forms of circulating water systems (civilian circulating water, industrial circulating water), with excellent performance and anti-corrosion life of up to 50 years; fire water supply systems, water supply and drainage transportation of various buildings, various chemical fluid transportation, and underground pipes and crossing pipes for wires and cables.

Plastic-coated steel pipes combine the excellent anti-corrosion properties of polyethylene and epoxy with the super anti-deformation ability of steel pipes. They have simple processes, convenient construction, high mechanical strength, and fully automatic coating equipment, which reduces the probability of recoating and rework, saves time and costs, is environmentally friendly, has a long service life, is safe and hygienic, has a wide range of applications, and has excellent anti-corrosion effects.

Safety Precautions For Anti-corrosion Steel Pipe Construction

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3PE anti-corrosion steel pipe spraying technology, most domestic 3PE anti-corrosion steel pipe production technology adopts the production and processing technology of “epoxy powder spraying, adhesive and polyethylene lateral extrusion, winding rolling”, because the powder and electrostatic thermal spraying method does not require rolling system, thus solving the problem of thin weld coating of spiral structure welded steel pipes, saving a large amount of plastic extruders and other mechanical equipment on the production line, and reducing production energy consumption.

Specific construction: The steel pipe after shot blasting and rust removal is heated to 210°C to 220°C at a moderate temperature, and the epoxy powder is still in a molten state. The adhesive and PE are extruded into thin sheets with an extruder, sprayed and wrapped around the steel pipe, and then flattened with a roller; the epoxy powder is in powder form, and the adhesive and PE are in granular form, and only electrostatic spraying and plasticization can be used Extrusion wrap.

There are many reasons for the bending of steel pipes, such as the thermal impact of the welding seam, eccentricity during forming, compression force, imbalance of bending force, etc. But fundamentally speaking, bending is the result of internal stress in the steel pipe. Simply put, bending is stress imbalance. So, does a straight steel pipe have no internal stress? no. Straight steel pipes also have internal stress, but the internal stress of straight pipes is smaller. ​

What is internal stress? Temperature, an interaction force between molecules that causes deformation due to the influence of external forces. When steel pipes are formed and welded, they will also be affected by external forces such as welding temperature and forming bending, resulting in internal stress. The cross-section of the steel pipe is an annular shape, and two basic stresses will be generated in this annular area: a force parallel to the annular shape and a force perpendicular to the annular shape. Parallel stresses will cause the tube to become out of round; vertical stresses will cause the tube to bend. Therefore, there is a cold diameter expansion process in the production process of straight seam steel pipes. The purpose is to eliminate the internal stress of the steel pipe and increase the strength of the straight seam steel pipes. ​

The pipe that needs to be straightened is fed into the lower roller of the straightening machine from the feeding device at the left end (or right end) of the machine. The upper roller moves downward to press the pipe and stop after reaching the corresponding position. The upper and lower rollers are respectively inclined at a certain angle with the axis of the straightened pipe. The hyperbolic generatrix of the rollers matches the outer diameter of the pipe and forms an envelope shape.

The three upper rollers are pressed against the pipe under the action of their respective hydraulic cylinders, and the two lower rollers are driven to rotate by their respective hydraulic motors, driving the pipe to both rotate around the axis and move along the axial direction. Changing the rotation direction of the hydraulic motor can change the rotation direction and axial movement direction of the pipe to achieve reversible straightening. The straightened pipe is then sent to the material rack through the discharging device at the other end. For pipes with large local bending deformation, the punches at both ends can be used to perform partial straightening first, and then perform overall straightening.

Characteristics And Inspection Of Internal And External Plastic-coated Steel Pipes

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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 pipes 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.

Storage Standards For Anti-corrosion Steel Pipes

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I believe many people have doubts about the storage of anti-corrosion steel pipes. Let’s take a look at the storage of anti-corrosion steel pipes.

1. The appearance of anti-corrosion steel pipes entering and leaving the warehouse needs to be inspected as follows:

① Inspect each root to ensure that the surface of the polyethylene layer is flat and smooth, with no dark bubbles, pitting, wrinkles, or cracks. The overall color needs to be uniform. There should be no excessive corrosion on the surface of the pipe.

② The curvature of the steel pipe should be <0.2% of the length of the steel pipe, and its ovality should be ≤0.2% of the outer diameter of the steel pipe. The surface of the entire pipe has local unevenness <2mm.

2. The following points need to be paid attention to when transporting anti-corrosion steel pipes:

① Loading and unloading: Use a hoist that does not damage the pipe mouth and do not damage the anti-corrosion layer. All construction tools and equipment must comply with regulations during loading and unloading. Before loading, the anti-corrosion grade, material, and wall thickness of the pipes should be checked in advance, and mixed installation is not advisable.

②Transportation: A thrust baffle needs to be installed between the trailer and the cab. When transporting anti-corrosion pipes, they need to be tied firmly and measures to protect the anti-corrosion layer should be taken in a timely manner. Rubber plates or some soft materials should be installed between the anti-corrosion pipes and the frame or columns, and between the anti-corrosion pipes.

3. What are the storage standards:

① Pipes, pipe fittings, and valves need to be properly stored according to the instructions. Pay attention to inspection during storage to avoid corrosion, deformation, and aging.

② There are also materials such as glass cloth, heat-wrap tape and heat-shrinkable sleeves that need to be stored in a dry and well-ventilated warehouse.

③ Pipes, pipe fittings, valves and other materials can be classified and stored in the open air. Of course, the storage site selected must be flat and free of stones, and there must be no accumulation of water on the ground. The slope is guaranteed to be 1% to 2%, and there are drainage ditches.

④ Anti-corrosion pipes in the warehouse need to be stacked in layers, and the height needs to ensure that the pipes do not lose their shape. Stack them separately according to different specifications and materials. Soft cushions should be placed between each layer of anti-corrosion pipes, and two rows of sleepers should be laid under the lower pipes. The distance between stacked pipes should be >50mm from the ground.

⑤ If it is on-site construction, there are some storage requirements for pipes: two support pads need to be used at the bottom, the distance between them is about 4m to 8m, the anti-corrosion pipe must not be less than 100mm from the ground, the support pads and anti-corrosion Pipes and anti-corrosion pipes must be padded with flexible spacers.