Steel pipes can be divided into two categories according to production methods, one is seamless steel pipes
, and the other is welded steel pipes
. Welded steel pipes can be divided into two types: straight seam welding and spiral welding according to the shape of the weld. According to different welding methods, welded steel pipes can be further divided into high-frequency welded pipes (HFW) and double-sided submerged arc welded pipes (DSAW).
First, let us focus on high-frequency welded pipes (HFW):
What is HFW steel pipe?
It should be noted that HFW pipe is a type of ERW pipe.
Features of high frequency welded pipe:
The diameter of high-frequency welded pipes is usually small and does not require threading of welding wire, so the possibility of cracking when expanding is very small. In terms of welding speed, for smaller outer diameters, such as those below 1 inch, the speed can be as high as 200 meters per minute. There are usually two methods of crimping, one is welding and the other is fusion welding. High-frequency welding is the first welding method. From a processing point of view, welding welded pipes mainly involves bending the steel plate into a cylinder and then welding it into shape. The method is simple and efficient.
Production principle of high frequency welded steel pipe:
According to the principle of electromagnetic induction and the skin effect, proximity effect and eddy current thermal effect of AC charges in the conductor, the steel at the welding edge is heated and melted, and then extruded with a roller to achieve the intergranular connection of the butt weld, thereby achieving the purpose of welding. High-frequency welding is a type of induction welding that does not require welding fillers, has no welding spatter, has a narrow welding heat-affected zone, beautiful welding shapes, and good welding mechanical properties. It has been widely used in steel pipe production.
High-frequency welding of steel pipes utilizes the skin effect and proximity effect of alternating current. After the steel (strip) is rolled and formed, a circular tube blank with a broken section is formed. One or a group of resistors (magnetic rods) are rotated near the center of the induction coil of the tube blank. The resistor and the opening of the tube blank form a Electromagnetic induction circuit. Under the action of the skin effect and proximity effect, a strong and concentrated thermal effect is generated at the edge of the opening of the tube blank, causing the edge of the weld to be rapidly heated to the temperature required for welding. After being extruded by the pressure roller, the metal melt realizes inter-crystal bonding and cools down. Finally, a strong butt weld is formed.
Features of double-sided submerged arc welded pipe (DSAW):
Double-sided submerged arc welded pipes require the use of welding wire. The weld seam is much longer than that of straight seam pipes, and the production efficiency will be much lower, but it may be stronger in terms of strength and pressure resistance. It also has other advantages, such as good automation. Secondly, the welding quality of the final product is higher due to its relatively strong performance in two aspects: heat exchange on the one hand and protective performance on the other.
The production process of high-frequency welded pipes is relatively simple, so relatively speaking, the production efficiency of high-frequency welded pipes is higher. However, based on the continuous development of double-sided submerged arc welded pipes, its production efficiency has also been further improved. In conclusion, both welding methods have their own advantages and disadvantages. High-frequency welded pipe has the advantages of low possibility of cracking, fast welding speed, simple welding forming method, and high production efficiency. The main advantages of double-sided submerged arc welded pipes are automation and high welding quality. In practical applications, which welding method should be selected also needs to be analyzed according to the specific situation.