First, what is the material of galvanized steel pipes?
Galvanized pipes, also known as galvanized steel pipes, are pipes made of steel pipes after galvanizing. Commonly used steel pipes for galvanizing include carbon steel 20, 45 steel; alloy steel Q345, 20Cr, 40Cr, 20CrMo, 30-35CrMo, 42CrMo, etc. Among the many materials, carbon structural steel is more suitable for galvanizing. The material requires low carbon, the addition of alloy elements mainly based on manganese, the addition of auxiliary elements such as niobium, titanium, or vanadium, and the addition of a small amount of rare earth elements.
Second, the types of galvanized steel pipes
Hot-dip galvanized steel pipes: Hot-dip galvanized steel pipes have the advantages of uniform coating, strong adhesion, and long service life. Most of the processes in the north use the galvanized strip direct coiling zinc supplementation process. Hot-dip galvanized steel pipes react with molten metal to produce an alloy layer, thereby combining the substrate and the coating. Is hot-dip galvanized steel pipe better or cold-dip galvanized steel pipe?
Cold-dip galvanized steel pipe: Cold-dip galvanizing is electro-galvanizing. The zinc layer of cold-dip galvanized steel pipe is electroplated, and the zinc layer is layered independently from the steel pipe substrate. The amount of galvanizing is very small, the zinc layer is thin, and the zinc layer is simply attached to the steel pipe substrate and is easy to fall off, so its corrosion resistance is poor. Therefore, in residential buildings, it should be prohibited to use cold-dip galvanized steel pipes as water supply pipes.
Third, the main uses of galvanized steel pipes
1. The application of hot-dip galvanized steel pipes has also expanded accordingly with the development of industry and agriculture. Therefore, hot-dip galvanized steel pipes are widely used in industry (such as chemical equipment, oil processing, marine exploration, metal structures, power transmission, shipbuilding, etc.), agriculture (such as sprinkler irrigation, greenhouses), construction (such as water and gas transmission, wire casing, scaffolding, houses, etc.), bridges, transportation, etc.
2. Due to certain defects, cold-dip galvanized steel pipes are now prohibited from being used as water and gas pipes and have withdrawn from the field of fluid transportation. However, cold-dip galvanized steel pipes are still used in some fire water and ordinary frame structures because the welding performance of this type of pipe is quite good. More>>
Fourth, galvanized steel pipe model specifications
Common galvanized steel pipe specifications and sizes are Model DN15, outer diameter 21.3mm. Model DN20, outer diameter 26.9mm. Model DN25, outer diameter 33.7mm. Model DN32, outer diameter 42mm. Model DN40, outer diameter 48.3mm. Model DN50, outer diameter 60.3mm.
Fifth, how to choose galvanized steel pipes
1. Look at the appearance: good galvanized steel pipes have a smooth appearance, no zinc nodules or burrs, and are generally silver-white; inferior galvanized steel pipes have no metallic luster, are light red or similar to the color of pig iron, and are prone to burrs, which are easy to scratch, and deep scratches reduce the strength of steel.
2. Weighing weight: high-quality galvanized steel pipes contain fewer impurities, have a high density of steel, and have a small size deviation. Weighing and checking them can determine the quality. Generally, considering the cumulative error, it is recommended that the whole phase weighing effect will be better.
3. Look at the performance: good galvanized steel pipes have no hydrogen embrittlement and no temperature hazards, which can ensure that the mechanical properties of the material remain unchanged, have good corrosion resistance, and the neutral salt spray test reaches 240. The weight of the zinc coating should not be less than 500g/㎡; inferior galvanized steel pipes often have meat loss on the cut end due to poor material, uneven, and the cross ribs of fake and inferior galvanized steel pipes are thin and low, and often appear incomplete.
4. Experiment: Conduct uniformity and cold bending tests on galvanized steel pipes. High-quality galvanized steel pipe samples will not turn red after being immersed in copper sulfate solution for 5 consecutive times. Galvanized steel pipes with a diameter of no more than 50mm should be subjected to cold bending tests with a bending angle of 90°.
5. Look at the price: How much does a ton of galvanized steel pipes cost? The price of hot-dip galvanized steel pipes is related to the specifications, materials, models, surface quality, finish, dimensional tolerance, thickness, and other factors of the galvanized steel pipes. The price is usually around 4,000-4,500 yuan per ton; if it is calculated by meter, the weight and length of the steel pipe should be considered and converted. More >>
Sixth, galvanized steel pipe welding skills
Generally speaking, galvanized steel pipe fittings can be welded. Ordinary galvanized steel pipes have a relatively thin galvanized layer. Ordinary electric welding or gas-shielded welding is used. Gas-shielded welding is mainly suitable for situations where grinding is not convenient and welding with a galvanized layer is required; if the galvanized layer is thick, argon arc welding with welding rods can be considered.
1. Before welding: The pre-welding preparation of galvanized steel is the same as that of general low-carbon steel. It mainly deals with the groove size and the nearby galvanized layer. The groove size is generally 60-65°, leaving a certain gap, generally 1.5~2.5mm; before welding, to reduce the penetration of zinc into the weld, the galvanized layer in the groove should be removed.
2. During welding: The welding technique adopts centralized groove making, and the process of not leaving blunt edges is centralized for control. The two-layer welding process reduces the possibility of incomplete welding. When welding, you should also pay attention to the following:
(1) When welding the first layer of multi-layer welds, try to melt the zinc layer and make it vaporize and evaporate to escape from the weld, which can greatly reduce the liquid zinc left in the weld.
(2) When welding fillet welds, also try to melt the zinc layer in the first layer and make it vaporize and evaporate to escape from the weld. The method is to first move the end of the electrode forward about 5~7mm, and then return to the original position and continue welding forward after the zinc layer is melted.
(3) When welding horizontally and vertically, it is recommended to use short-slag electrodes such as J427, so that the edge biting tendency will be small; the forward and backward reciprocating electrode technology is used to improve the welding quality.
3. After welding: After welding, the galvanized layer of the galvanized steel pipe must be polished off at the welding point, otherwise bubbles, sand holes, false welding, and other problems will occur, and the weld will become brittle and the rigidity will decrease. More>>
Seventh, will galvanized steel pipes rust?
Not easy to rust. Ordinary steel pipes are exposed to the air, and they react with oxygen to oxidize, or they are corroded by oxygen elements in the water to become oxides, which will rust. Galvanized steel pipes are galvanized to form a layer of galvanized layer to isolate the air, so they are more corrosion-resistant and less likely to rust. Generally speaking, galvanized steel pipes are not easy to rust, but it does not mean that they will not rust. It is just a matter of time. After a long time of use, galvanized steel pipes will still rust; in addition, if the environment of use is relatively humid, or if it is exposed to rain for a long time, the galvanized steel pipe will quickly oxidize and spot, and then will rust. In addition, there are two types of galvanized steel pipes: hot-dip galvanized steel pipes and cold-dip galvanized steel pipes. Relatively speaking, hot-dip galvanized steel pipes are less likely to rust than cold-dip galvanized steel pipes.
Post time: Nov-15-2024