How To Clean Internal And External Plastic-coated Steel Pipes

There is a cleaning and cleaning step in the maintenance of internal and external plastic-coated steel pipes, so the cleaning step is also very important. How can it be implemented well? Steel Pipe has some detailed introduction in these aspects. I hope everyone can learn this.

Cleaning of internal and external plastic-coated steel pipes uses solvents and emulsions to clean the surface of the steel to achieve the effect of removing oil, grease, dust, lubricants and similar organic matter. However, it cannot remove rust, oxide scale, welding flux, etc. on the surface of the steel, so it is not suitable for anti-corrosion production. It is only used as an auxiliary method. Rust removal: First, use tools such as wire brushes to polish the surface of the steel to remove loose or lifted oxide scale, rust, welding slag, etc.

The rust removal of hand tools can reach Sa2 level, and the rust removal of power tools can reach Sa3 level. If the surface of the steel is adhered to a strong iron oxide scale, the rust removal effect of the tool will not be ideal and the anchor pattern depth required for anti-corrosion construction will not be reached. Pickling: Chemical and electrolytic methods are generally used for pickling treatment. Only chemical pickling is used for pipeline anti-corrosion, which can remove scale, rust, and old coatings. Sometimes it can be used as a reprocessing after sand blasting and rust removal.

Although chemical cleaning can make the surface reach a certain degree of cleanliness and roughness, its anchor lines are shallow and it is easy to cause contamination. Spray (throw) rust removal: Spray (throw) rust removal uses a high-power motor to drive the spray (throw) blade to rotate at high speed, so that abrasives such as steel sand, steel shots, iron wire segments, minerals, etc. are sprayed internally and externally under the effect of centrifugal force. The surface of the plastic-coated pipe is sprayed (thrown), which not only can completely remove rust, oxides and dirt, but also the internal and external plastic-coated pipes can achieve the required uniform roughness under the action of strong abrasive impact and friction. .

The reason is that when steel is alloyed with chromium, the type of surface oxide is changed to a surface oxide similar to that formed on pure chromium metal. When the addition amount of chromium reaches 10.5%, the atmospheric corrosion resistance of the equal-diameter tee is significantly increased. However, when the chromium content is higher, although the corrosion resistance can still be improved, it is not significant. Moreover, if the surface layer is damaged, the exposed steel surface will repair itself by reacting with the atmosphere, re-forming the oxide, and continuing to provide protection. Steel-plastic pipes must use cathodic maintenance while using anti-corrosion coatings.

After the rust removal treatment on the surface of the steel plate, 95% of the surface area is removed from visible rust, and 5% of the area and original rust spots remain. Use an alloy steel shovel to remove the old paint on the gas tank. This oxide layer is extremely thin, and the natural luster of the surface of the elbow can be seen through it, giving the elbow a unique surface. Use a wire brush to remove internal rust from welds, reinforcement plates and other dead ends.

The adhesion of the coating to the substrate is an important indicator for evaluating the corrosion resistance of the coating. The stronger the adhesion, the better the corrosion resistance, and the more durable the coating. After the surface treatment is completed, apply epoxy coal pitch primer twice to prevent moisture and rust. Use acetone or other volatile cleaning agents to remove oil, tar and other dirt on the surface of the gas tank. Clean the internal and external plastic-coated steel pipes. After cleaning, the surface should be dry, oil-free and dirt-free.

Characteristics Of Conventional Galvanized Layers

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.

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

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.

Check The Process Of Plastic Coated Steel Pipes

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.

Forming Process Of Straight Seam Welded Steel Pipe

In terms of welding technology, straight seam steel pipes can be divided into resistance welded straight seam steel pipes and submerged arc welding straight seam steel pipes. Resistance welded straight seam steel pipes are further divided into high frequency welded straight seam steel pipes, medium frequency welded straight seam steel pipes, and low frequency welded straight seam steel pipes. The submerged arc welded straight seam steel pipe is also called double-sided submerged arc welded straight seam steel pipe or LSAW straight seam steel pipe, where LSAW is (the abbreviation of Longitudinally Submerged Arc Welding is LSAW).

Electric resistance welded straight seam steel pipe is also called ERW straight seam steel pipe. ERW is (Electric Resistance Weldin), and the abbreviation is ERW. High frequency welded straight seam steel pipe is also called ERW straight seam steel pipe. ERW is a general term for resistance welded steel pipes. Straight seam high-frequency resistance welding pipe (Electric Resistance Welding, referred to as ERW) ERW is the first letter of the corresponding English word.

Resistance welded steel pipes are divided into two forms: AC welded steel pipes and DC welded steel pipes. AC welding is divided into low frequency welding, medium frequency welding, super medium frequency welding and high frequency welding according to the frequency. High-frequency welding is mainly used for the production of thin-walled steel pipes or ordinary-walled steel pipes. High-frequency welding is divided into contact welding and induction welding. DC welding is generally used for small diameter steel pipes.

The main steps are as follows:

1. Plate detection: After the steel plates used to manufacture large-diameter submerged arc welded straight seam steel pipes enter the production line, they are first subjected to full-plate ultrasonic inspection;

2. Edge milling: Use an edge milling machine to perform double-sided milling on both edges of the steel plate to achieve the required plate width, plate edge parallelism and bevel shape;

3. Pre-bending edge: Use a pre-bending machine to pre-bend the edge of the board so that the edge of the board has a curvature that meets the requirements;

4. Forming: On the JCO forming machine, first half of the pre-bent steel plate is stamped into a “J” shape through multiple steps, and then the other half of the steel plate is similarly bent into a “C” shape, and finally the opening is formed. “O” shape

5. Pre-welding: join the formed straight seam welded steel pipes and use gas shielded welding (MAG) for continuous welding;

6. Internal welding: Use longitudinal multi-wire submerged arc welding (up to four wires) to weld the inside of the straight seam steel pipe;

7. External welding: tandem multi-wire submerged arc welding is used to weld the outside of the longitudinal submerged arc welded steel pipe;

8. Ultrasonic inspection I: 100% inspection of the internal and external welds of the straight seam welded steel pipe and the base metal on both sides of the weld;

9. X-ray inspection I: 100% X-ray industrial television inspection of internal and external welds, using an image processing system to ensure the sensitivity of flaw detection;

10. Diameter expansion: The entire length of the submerged arc welded straight seam steel pipe is expanded to improve the dimensional accuracy of the steel pipe and improve the distribution of stress within the steel pipe;

11. Hydraulic pressure test: The expanded steel pipes are inspected one by one on a hydraulic pressure testing machine to ensure that the steel pipes meet the test pressure required by the standard. The machine has automatic recording and storage functions;

12. Chamfering: Process the pipe end of the steel pipe that has passed the inspection to achieve the required pipe end bevel size;

13. Ultrasonic inspection II: Conduct ultrasonic inspection one by one again to check for defects that may occur after diameter expansion and hydraulic pressure of the straight seam welded steel pipes;

14. X-ray inspection II: X-ray industrial television inspection and pipe end weld photography on the steel pipe after diameter expansion and hydraulic pressure test;

15. Magnetic particle inspection of pipe ends: This inspection is performed to detect pipe end defects;

16. Anti-corrosion and coating: Qualified steel pipes will be anti-corrosion and coated according to user requirements.

Heating oxidation defects and control of galvanized steel pipe heating furnace

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.

Do Hot-dip Galvanized Steel Pipes Need To Be Painted?

Generally, galvanized pipes do not need to be painted. If they are painted, they are usually painted with silver paint. After the steel pipe is galvanized, the surface is covered with a layer of zinc coating, which isolates the steel pipe from the atmosphere, avoids direct contact and corrosion of the steel pipe by the atmosphere, and is protected. As for the zinc coating on the surface of the steel pipe, due to the relatively strong chemical activity of zinc, a thin and dense layer of zinc carbonate will be formed in the air at room temperature to protect the zinc itself from further oxidation.

Therefore, galvanized pipes, both the surface zinc and the steel pipe itself, are protected from rust and do not need to be painted with anti-rust paint. Only when the galvanized layer is damaged (such as steel pipe welding and the coating at the joint is burned) and the steel pipe is exposed to the air and loses the protection of the galvanized layer, is it necessary to reapply anti-rust paint.

The substrates (anti-rust primers) suitable for galvanized parts include epoxy zinc yellow primer (two-component) and epoxy ester zinc yellow primer. Galvanized parts are non-ferrous metals, and non-ferrous metals have poorer adhesion than black all-metal. Commonly used alkyd iron red primers and epoxy iron red primers on the market are not suitable for use on galvanized parts, otherwise they will easily fall off. It should be pointed out in particular that when alkyd paint is used on galvanized parts, a saponification reaction will occur. Not only will the coating fail, but the original galvanized layer will also be damaged.

Pre-treatment when painting galvanized parts:

1. If possible, you can phosphate the galvanized parts, or spray a thin layer of phosphating primer first.

2. Or sand-sweep the surface of smooth galvanized parts.

3. Wipe the surface of galvanized workpieces and galvanized pipes with solvent (i.e. epoxy zinc yellow primer diluent) to remove the protective layer of crude oil on the workpiece and increase cleanliness.

4. Two-component epoxy zinc yellow primer: Prepare the paint strictly according to the ratio of paint and curing agent, and after curing for 30 minutes, adjust the appropriate construction viscosity before spraying. One-component epoxy ester zinc yellow primer: adjust the appropriate construction viscosity and apply it with the correct construction method.

New Patching Method For Epoxy Coal Pitch Anti-corrosion Steel Pipes

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.

Protective Measures For Insulated Pipes


In engineering, industry, chemical industry or home, pipe insulation is the most common way, and the closest thing to life is the insulation of heating pipes. Polyurethane direct-buried insulation pipes are used in thermal and cold insulation projects for various indoor and outdoor pipelines, central heating pipelines, central air-conditioning pipelines, chemical industry, medicine and other industrial pipeline
Overview: Since the birth of polyurethane synthetic materials in the 1930s, polyurethane foam insulation pipes have been developing rapidly as an excellent thermal insulation material. Its application range has become more and more extensive, especially because of its simple construction, energy-saving and anti-corrosion effects. It is widely used in various pipelines such as heating, refrigeration, oil transportation, and steam transportation. It is widely used in various pipelines such as heating, refrigeration, oil transportation, and steam transportation. It not only provides a normal transportation method for heating pipes, but also has a certain degree of safety.
However, after insulating the pipeline, attention should also be paid to protective measures.
If there is no good sealing effect, such as cracks or sudden occurrences, after the insulated pipe is insulated, it will lead to insufficient insulation and even severe freezing damage, which will also affect the way the pipe works. Therefore, when insulating pipes, their sealing effect must be ensured.
The next step is to pay attention to monitoring after pipe insulation. Good insulation materials for prefabricated polyurethane insulation pipes should have low thermal conductivity; they will not deteriorate when exposed to moisture, have good heat resistance, do not corrode metal, are lightweight and have many gaps; have certain mechanical strength and will not be damaged when subjected to external forces; Easy to process and low cost.
Commonly used insulation materials include: expanded perlite and its products, glass wool and its products, rock wool products, microporous calcium silicate, aluminum silicate fiber products, foam plastics, foamed asbestos, etc.
This project is relatively simple, that is, irregular or regular inspections to ensure the effectiveness of the insulation effect, and is also conducive to protection inspections, thereby achieving better protection effects.
Special attention should be paid to protective measures after pipeline insulation, especially regular monitoring measures. This not only allows us to grasp the insulation status in time, but also ensures the safety and effectiveness of pipeline work and detects problems in time to avoid serious consequences. Therefore, when it comes to pipeline insulation, we must pay attention to the above conditions.

The Basic Method Of Steel Pipe Derusting

Long-distance oil and gas pipelines are an important means of energy security. During the anti-corrosion construction process of oil (gas) pipelines, the surface treatment of steel pipes is one of the key factors that determine the anti-corrosion service life of the pipelines. It is the prerequisite for whether the anti-corrosion layer and the steel pipe can be firmly combined. . It has been verified by research institutions that, in addition to factors such as coating type, coating quality, and construction environment, the surface treatment of steel pipes accounts for about 50% of the impact on the life of the anti-corrosion layer. Therefore, the anti-corrosion layer specifications should be strictly followed. The requirements for the surface of steel pipes are constantly explored and summarized, and the surface treatment methods of steel pipes are constantly improved. the

1. Cleaning

Solvents and emulsions are used to clean the steel surface to remove oil, grease, dust, lubricants and similar organic matter. However, it cannot remove rust, oxide scale, welding flux, etc. on the steel surface, so it is only used as an auxiliary means in anti-corrosion production. the

2. Tool derusting

Mainly use tools such as wire brushes to polish the steel surface to remove loose or lifted oxide scale, rust, welding slag, etc. The rust removal of hand tools can reach Sa2 level, and the rust removal of power tools can reach Sa3 level. If the iron oxide scale is firmly attached to the surface of the steel, the rust removal effect of the tool will not be ideal and the anchor pattern depth required for anti-corrosion construction will not be achieved. ​

3. Pickling

Generally, chemical and electrolytic methods are used for pickling treatment. Only chemical pickling is used for pipeline anti-corrosion, which can remove scale, rust, and old coatings. Sometimes it can be used as a reprocessing after sandblasting and rust removal. Although chemical cleaning can achieve a certain degree of cleanliness and roughness on the surface, its anchor lines are shallow and it can easily cause environmental pollution. the

4. Spray (throw) to remove rust

Spraying (throwing) rust removal uses a high-power motor to drive the spraying (throwing) blades to rotate at high speed, so that steel sand, steel shots, wire segments, minerals and other abrasives are sprayed (throwing) on the surface of the steel pipe under the action of centrifugal force. , not only can rust, oxides and dirt be completely removed, but the steel pipe can also achieve the required uniform roughness under the action of violent impact and friction of abrasives. After spraying (throwing) rust removal, it can not only expand the physical adsorption on the pipe surface, but also enhance the mechanical adhesion between the anti-corrosion layer and the pipe surface. Therefore, spraying (throwing) rust removal is an ideal rust removal method for pipeline anti-corrosion.

4.1 Derusting level

For the construction technology of epoxy, vinyl, phenolic and other anti-corrosion coatings commonly used for steel pipes, the surface of the steel pipe is generally required to reach near white level (Sa2.5). Practice has proven that using this level of rust removal can remove almost all oxide scale, rust and other dirt. The depth of the anchor pattern can reach 40-100µm, which fully meets the adhesion requirements between the anti-corrosion layer and the steel pipe. However, spraying (throwing) can remove The rust process can achieve near-white level (Sa2.5) technical conditions with lower operating costs and stable and reliable quality.

4.2 Spraying (throwing) abrasives

In order to achieve the ideal rust removal effect, the abrasive should be selected according to the hardness of the steel pipe surface, the original rust degree, the required surface roughness, the coating type, etc. For single-layer epoxy, two-layer or three-layer polyethylene coatings, use The mixed abrasive of steel sand and steel shot is easier to achieve the ideal rust removal effect. Steel shot has the function of strengthening the steel surface, while steel grit has the function of etching the steel surface. Mixed abrasives of steel grit and steel shot (usually the hardness of steel shot is 40 to 50 HRC, and the hardness of steel grit is 50 to 60 HRC) can be used on various steel surfaces, even on grade C and D rusted steel surfaces. , the rust removal effect is also very good.

4.3 Abrasive particle size and ratio

In order to obtain better uniform cleanliness and roughness distribution, the particle size and proportion design of the abrasive are very important. Too much roughness will easily cause the anti-corrosion layer to become thinner at the peaks of the anchor lines; at the same time, because the anchor lines are too deep, bubbles will easily form in the anti-corrosion layer during the anti-corrosion process, seriously affecting the performance of the anti-corrosion layer. If the roughness is too small, the adhesion and impact strength of the anti-corrosion layer will decrease. For severe internal pitting corrosion, we cannot rely solely on high-intensity impact with large-grain abrasives. We must also rely on small particles to grind away the corrosion products to achieve the cleaning effect. At the same time, reasonable ratio design can not only slow down the wear of the abrasives on the pipes and nozzles (blade) , and the utilization rate of abrasive can be greatly improved. Usually, the particle size of steel shot is 0.8~1.3 mm, and the particle size of steel sand is 0.4~1.0 mm, of which 0.5~1.0 mm is the main component. The ratio of sand to shot is generally 5-8.

It should be noted that in actual operation, the ideal ratio of steel grit and steel shot in the abrasive is difficult to achieve because the hard and brittle steel grit has a higher breakage rate than the steel shot. For this reason, the mixed abrasives should be continuously sampled and tested during operation, and new abrasives should be added to the rust remover according to the particle size distribution. Among the new abrasives added, steel grit should account for the majority.

4.4 Derusting speed

The rust removal speed of the steel pipe depends on the type of abrasive and the displacement of the abrasive, that is, the total kinetic energy E applied to the steel pipe by the abrasive per unit time and the kinetic energy E1 of the single-grain abrasive. the

Generally, abrasives with lower loss rates should be selected, which will help improve the cleaning speed and extend the life of the blades.

4.5 Cleaning and Preheating

Before spraying (throwing) treatment, use cleaning methods to remove grease and scale on the surface of the steel pipe, and use a heating furnace to preheat the pipe body to 40-60°C to keep the surface of the steel pipe dry. During spraying (throwing) treatment, since the surface of the steel pipe does not contain grease and other dirt, the rust removal effect can be enhanced. The dry steel pipe surface is also conducive to the separation of steel shot, steel sand, rust and oxide scale, making the rust removed The steel pipe surface is cleaner.

5.Conclusion

Pay attention to the importance of surface treatment in production and strictly control the process parameters during rust removal. In actual construction, the peel strength value of the anti-corrosion layer of the steel pipe greatly exceeded the standard requirements, ensuring the quality of the anti-corrosion layer. On the basis of the same equipment, , greatly improving the process level and reducing production costs.