Welding Principle of ERW Steel Pipe

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Substantial-frequency welding originated in the 1950s. It is a new variety of welding approach that utilizes the skin effect and proximity result developed by higher-frequency existing to connect steel plates and other metal materials. The emergence and maturity of substantial-frequency welding technological innovation has straight promoted the huge growth of the longitudinally welded pipe business. It is a crucial method in the production of ERW steel pipe. The good quality of large-frequency welding directly impacts the overall strength, top quality level and production pace of welded pipe goods.

Fundamental ideas of high frequency welding

The so-named higher frequency is relative to the frequency of the alternating existing of 50Hz, and normally refers to the substantial frequency recent of 50KHz~400KHz. When high-frequency existing passes by way of a metal conductor, two peculiar effects are developed: skin effect and proximity impact. Substantial-frequency welding employs these two effects to weld steel pipes. So, what are these two effects?

Skin result:


Refers to when a specific frequency of alternating recent passes by way of the exact same conductor, the density of the recent is not evenly distributed across all sections of the conductor, it will primarily focus on the surface of the conductor, that is, the density of the present on the surface of the conductor is substantial, and the density inside the conductor Tiny, so we vividly phone it: "skin effect". The skin result is typically measured by the penetration depth of the existing. The smaller the penetration depth, the much more considerable the skin impact. This penetration depth is proportional to the square root of the resistivity of the conductor, and inversely proportional to the square root of frequency and permeability. In layman's terms, the increased the frequency, the much more current is concentrated on the surface of the steel plate the reduced the frequency, the more scattered the surface present. It have to be noted that even though steel is a conductor, its magnetic permeability will lessen as the temperature rises. That is to say, when the temperature of the steel plate increases, the magnetic permeability will decrease and the skin result will reduce.

Proximity impact:
Refers to when large-frequency recent flows in opposite instructions in between two adjacent conductors, the present will flow intensively to the edges of the two conductors. Even if the two conductors have one more shorter side, the present does not stick to the shorter side. Route movement, we call this impact: "proximity result". The proximity impact is primarily due to the role of inductive reactance, which plays a major position in high-frequency currents. The proximity result increases as the frequency increases and the distance between adjacent conductors gets to be closer. If a magnetic core is added all around the adjacent conductor, the higher-frequency present will be a lot more concentrated on the surface of the workpiece.

These two results are the basis for realizing large-frequency metal welding. Higher-frequency welding utilizes the skin result to concentrate the power of the high-frequency recent on the surface of the workpiece and uses the proximity impact to handle the location and variety of the large-frequency present flow path. Source Link The pace of the current is very rapidly, it can heat and melt the edges of adjacent steel plates in a short time, and comprehend the butt joint by way of extrusion.

Ideas: ASTM A53 Grade B is much more common than other grades. These pipes can be bare pipes without having any coating, or it might be Sizzling-Dipped or Zinc-Coated and produced by Welding or by a Seamless manufacturing approach. In Oil and Fuel, A53 grade pipes are used in the structural and non-vital applications.