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%.

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.

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.

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.

When plated parts need to be stacked closely together for storage and transportation, adequate precautions should be taken to prevent white rust. Maintaining a low humidity environment around the plated parts and ensuring adequate ventilation between stacked plated parts can prevent white rust. Minimize it. Specific precautions are described below.

one. Surface treatment can be used to reduce the occurrence of white rust on the coating. Galvanized pipes and hollow plated parts can be coated with a layer of varnish after galvanizing. Products such as wires, plates and mesh materials can be waxed and oiled. Hot-dip galvanized structural parts can be subjected to chromium-free passivation after water cooling. deal with. If the plated parts can be transported and installed quickly, no post-processing is required.

In fact, whether hot-dip galvanizing requires surface treatment mainly depends on the shape of the plated parts and possible storage conditions. Plated parts that are tightly stacked or nested have poor protection against white rust, especially when they are stored for more than several weeks. Of course, if the surface of the galvanized structural part is fully exposed, post-processing is generally not required. If the galvanized surface is to be painted within 6 months, an appropriate post-treatment process must be selected to avoid affecting the adhesion between the zinc layer and the paint.

two. Plated parts should be stored in a covered storage room in a dry, well-ventilated environment.

three. If the plated parts can only be stored in the open air, the plated parts should be elevated from the ground and separated by narrow spacers to provide free flow of air to all plated parts surfaces. Plated parts should be placed at an angle to facilitate drainage. Plating should not be stored on wet soil or rotting vegetation. Separators are also recommended when shipping, if condensation is likely to occur on the surface of the plated part.

In addition, if the plated parts will cool down when transported over high mountains and then exposed to warmer and moister air at ground level, insulators must be used in this case. Wood containing rosin cannot be used as insulation or packaging because rosin itself is corrosive. It is recommended to use dry, untreated wood such as poplar, locust and fir when transporting and storing plated parts. Small plated parts stored in containers should be dried thoroughly before packaging. When sealing with packaging boxes, it is recommended to add some desiccant.

Four. Do not place covered plated parts where they may be affected by rain, fog, condensation and snow.

five. When galvanized steel is shipped by sea, they should not be checked as surface cargo, nor should they be placed in the ship’s bilge where they may come into contact with bilge water. Under electrochemical corrosion conditions, seawater intensifies white rust corrosion. At sea, especially in tropical oceans, where humidity is high, it is particularly important to provide a dry environment and good ventilation facilities.