What is a galvanized steel pipe?
What is a galvanized steel pipe?
Galvanized pipe, also known as galvanized steel pipe, is divided into hot-dip galvanizing and electro-galvanizing. The hot-dip galvanizing layer is thick, with uniform plating, strong adhesion and long service life. The cost of electroplating is low, the surface is not very smooth, and its corrosion resistance is much worse than that of hot-dip galvanized pipes.
Hot dip galvanized pipe
The molten metal is reacted with an iron matrix to produce an alloy layer, thereby combining the substrate and the plating layer. Hot-dip galvanizing is to pickle the steel pipe first, in order to remove the iron oxide on the surface of the steel pipe, after pickling, it is washed by ammonium chloride or zinc chloride aqueous solution or a mixed aqueous solution of ammonium chloride and zinc chloride, and then fed. Hot dip plating tank. Hot-dip galvanizing has the advantages of uniform plating, strong adhesion and long service life. Most of the northern processes use galvanized strips to directly coil the zinc.
Cold galvanized pipe
Cold galvanizing is electrogalvanizing. The amount of galvanizing is very small, only 10-50g/m2, and its corrosion resistance is much worse than that of hot-dip galvanized pipes. Regular galvanized pipe manufacturers, in order to ensure quality, most do not use electro-galvanizing (cold plating). Only small companies with small equipment and old equipment use electro-galvanized steel, of course, their prices are relatively cheaper. In newly built houses, the use of cold-galvanized steel pipes as water supply pipes is prohibited.
Difference hot-dip galvanizing and cold galvanizing
Hot dip galvanizing process:
Workpiece degreasing → washing → pickling → washing → drying solvent dip fluxing preheated hot dip galvanized → cooling → finishing → rinsing → drying → passivation test
Chemical degreasing → washing → hot water hot water electrolysis degreasing → washing → washing → strong corrosive galvanized iron alloy → washing → washing → light → → washing → drying passivation
Appearance of hot-dip galvanizing and cold galvanizing
Cold galvanizing looks more smooth, bright, color passivation process plating layer is yellow-green in color, was colorful. Plating layer was bluish-white or white with white passivation process was green, white coating passivation process and the sun was significant Colorful angle. The complex workpiece angular edges parts prone to “electrical burning” from gloomy, the parts of the zinc layer thick. Yin corner site is easy to form a current dead undercurrent gray area and the area zinc layer is thinner. The workpiece overall zinc tumor, caking phenomenon.
Hot dip galvanized look a little rough compared to the electro-galvanized, silvery white, look prone process waterlines and a few drops of tumor is more obvious, especially in the one end of the workpiece. Hot dip galvanized zinc layer than a few times of the electro-galvanized thick corrosion protection is several times that of the electro-galvanized.
Characteristics of galvanized steel welding
Galvanized steel is generally low carbon steel plated with zinc, the zinc coating is generally 20um thick. At 419 ° C, the boiling point of about 908 ° C melting point of zinc. In welding, the melted liquid zinc bath floating on the surface or in the root of the weld location. Zinc has a greater solubility in iron, zinc etching liquid will go into the weld metal along the grain boundaries, low-melting zinc to form a “liquid metal embrittlement.” Meanwhile, zinc and iron brittle intermetallic compounds can be formed, these brittle phases so that the weld metal plastic lower under tensile stress and cracks. If the fillet weld, especially the fillet weld T-joints most prone to penetrate the cracks. When welding galvanized steel, zinc layer and the surface of the groove at the edge of the arc under the action of heat, oxidation, melting, evaporation as well as volatile white smoke and steam, can easily cause weld porosity. ZnO due to oxidation and the formation of its high melting point of about 1800 ° C or more, if small parameter in the welding process, will cause the ZnO slag, at the same time. Since Zn become deoxidizer. Produces FeO-MnO or FeO-MnO-SiO2 low melting point oxide slag. Second, due to the evaporation of zinc, volatile lot of white smoke, to stimulate the human body, harmful effects, therefore, must be welded zinc coating at the polished off.
Welding process control
Preparation before welding galvanized steel and low carbon steel is generally the same, you need to pay attention is to seriously handle the groove dimensions and the nearby zinc coating. For penetration, groove size should be appropriate, generally 60 ~ 65 °, to leave some space, usually 1.5 ~ 2.5mm; zinc in order to reduce the penetration of the weld, before welding can be galvanized inside groove Clear after layer and then welded. In practice, supervision, using a centralized playing groove, leaving blunt edge technology for centralized control, two welding process, reducing the possibility of incomplete penetration.
Galvanized pipe welding rod should be based on the choice of substrate material, usually low-carbon steel on account ease, use J422 is more common.
Welding techniques: When welding the first layer of the multilayer welding seam, try to make it melt and vaporize the zinc layer, evaporation and escape the weld, can greatly reduce the liquid zinc to remain in the weld. When fillet welds, as far as possible in the first layer to melt and vaporize the zinc coating, evaporation and escape the weld, the method is first removed from the ends of the electrode forward about 5 ~ 7mm, when the zinc layer melted down and continue to move back to the original position welding. Again when horizontal welding and vertical welding, such as welding slag, such as the choice of short-J427, undercut tends to be minimal; roundtrip transportation around if strip technology, but can be defect-free weld quality.
Galvanized Steel Pipe Production Line for Special Demands
For galvanized steel pipe production lines have special requirements, especially in a production environment this, a good environment can help us better production, improve production quality and production efficiency, particularly galvanized steel that needs a stable environment products even more so.
First, Ensure that the production line for delicate work processes, equipment, heating, ventilation, drainage, etc., all work must center around quality galvanized steel to expand, as long as the quality of the galvanized steel to ensure good, all other factors we can be achieved.
Galvanized steel currently use is very widespread, especially in natural gas pipes, heating and other high strength and quality of the pipeline industry, galvanized steel pipe has a more obvious than other advantages. Galvanized steel as plumbing, a large amount of rust inner tube after several years of use, the outflow yellow water pollution is not only ware, and mixed with not smooth inner wall of the breeding of bacteria, corrosion caused by heavy metal content in the water is too high, serious harm to human health. In order to make galvanized steel with a bright white appearance and good corrosion resistance, in addition to hot dip galvanizing process, you can also use electric galvanizing process.
Requirements of galvanized insulated steel pipe in construction:
1, Galvanized insulated steel pipe is used for gas and natural gas, long-distance transmission of high pressure pipeline.
2. Galvanizing in order to preserve corrosion, in the long-distance transportation, the pole protection testing station is generally set up at several tens of kilometers to 100 kilometers. The instrument in the station generates cathode electrons to fill the pipeline, and the galvanized surface is conducive to conductive rust. The pipe is charged uniformly.
3, In order to prevent the loss of cathode electrons in the pipeline, the galvanized pipe is filled with electric tannin (mixture of bitumen and quartz powder) and kraft paper, second oil two paper or three oil three papers before installation. After head welding, it should be treated equally. The insulation resistance should be not less than 0.5 Mn, and check if the pipe is punctured with low voltage 380V/220V.
4. On the side of the gas transmission pipeline, a distance of 50cm, a tens of meters of grounded galvanized l” pipe grounding tape shall be embedded in the same trench, and a galvanized iron tape shall be introduced into the testing station.
5. If the gas or natural gas leaks and breaks through the insulating layer under pressure, the electrons enter the land, return to the grounding zone and enter the detection instrument, and immediately reflect it from the instrument. The leak distance and the position of the pipe fault can be organized to repair the manpower.
Advantages of galvanized pipes are following below:
Firstly, galvanized pipe after being hot dip galvanized surface can be protected, and inside the cavity of the pipe or any other coating the corner is difficult to enter, deepen the zinc can easily cover to the top, make whole galvanized pipe can be protected.
Second, after being galvanized pipe galvanized its impact resistance and anti-wear properties are very good, because the zinc coating hardness values larger than the hardness of steel, and therefore the impact resistance of hot-dip galvanized after and abrasion resistance is quite good. Furthermore galvanized biggest advantage is in the corner of the zinc layer will be relatively thick and good toughness and abrasion resistance, while other coatings are often in this corner of the thinnest most difficult construction, and therefore are vulnerable injury.
Third, there is a major feature of hot-dip galvanizing that is occasionally subject to considerable mechanical damage or other causes a small portion of the zinc layer off, the iron-based nudity, then it will play around the zinc layer and other coatings not the same spirit of sacrifice to protect the steel here, so from erosion.
Finally, the hot-dip galvanizing and other aspects of life and aesthetics of art, life expectancy is in a particular environment, the main agency of the thickness of the coating, and the coating thickness of it but also by the thickness of the galvanized pipe and decisions, and therefore thicker galvanized pipe is more easily coating. Second, in terms of aesthetics and art, at the time it is certain severe corrosive environments, galvanized layer above Zaishi paint to deal with, as long as the selection of the correct paint system, easy construction of its anti-corrosion effect will be very good.
Difference between Black Steel Pipe and Galvanized Steel Pipe
Black steel pipe and galvanized steel pipe are the two most common kind of pipe applied to transport liquid and gas. They have several respects similar to each other and many people confuse one to the other one. What is the main difference between black steel pipe and galvanized steel pipe? Black steel pipe and galvanized pipe are made of steel, but galvanized pipe has a zinc coating while black pipe does not and therefore, galvanized pipe is more expensive and more durable. For transportation, black steel pipe tend to erode more easily than galvanized pipe and on account of this, it is more suitable for transporting gas and galvanized pipe is fit for carrying water instead of gas.
Galvanized pipe covered with a layer of zinc which makes it have higher ability of corrosion protection and help to prevent the accumulation of mineral deposits that will block the pipe. Galvanized pipe is mainly used for carrying water to supply home and commercial buildings; it is also serve as scaffolding frames because of its rust prevention. Black steel pipe is manufactured as seamless which makes it a better type for gas transportation. It can be used for fire sprinkler system since it can prevent fire better than galvanized pipe. Since it has a dark color surface that is form by iron oxide during the manufacturing process, it is called black steel pipe. The main difference between steel pipe and galvanized pipe lies in the surface. Black steel pipe is uncoated and made without steam, and therefore, it is widely used for transporting gas like propane and natural gas to residential and commercial building.
Galvanized pipe has zinc on the surface so the mineral will flack off as time goes by and block the pipe. This will lead to a burst. In view of this, transport gas by galvanized pipes is dangerous so it is often used in carrying water. Black steel pipe, on the other hand, is not suitable for water transport. Black steel pipes are tending to corrode in water and mineral of the pipe will dissolve into the water and clog the line as well.
General speaking, black steel pipe is cheaper than galvanized pipe. This is due to the zinc coating on galvanized pipe and the manufacturing process making it. Black steel pipe is low maintenance; it costs less to the fitting. Black steel pipe and galvanized steel pipe looked similar in the eye of many people. So how to differentiate this two pipe? Here are three main methods. First, you can examine the color of the pipe. Black steel pipe is darker than galvanized pipe; it is flat black while galvanized pipe is silver and gray. Second, galvanized pipe is usually applied for water carriage and black steel pipe for gas deliver, you can tell the difference by the material they carry. And last, you can tell from the year the pipe being used. Black steel pipe used later than galvanized pipe. If the pipe is installed after 1950s, it’s likely to be black steel.
Source: China Galvanized Steel Pipe Manufacturer – Yaang Pipe Industry Co., Limited (www.pipelinedubai.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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