What is the difference between HFW steel pipe and ERW steel pipe?

The same product, the same manufacturing process, the full English name: High Frequency (high frequency) Electric Resistance (resistance) Welding (welding), the full Chinese name: high frequency resistance welded pipe, because only straight seams can produce this type.
The main difference between ERW (straight seam resistance welding) and HFW (high frequency welding) is the principle.
About ERW

Resistance welding, as the name implies, is a method in which pressure is applied through electrodes after the weldment is assembled, and the resistance heat generated by the current passing through the contact surface of the joint and the adjacent area is used for welding. High-frequency welding: When high-frequency current passes through metal conductors, two peculiar effects will occur: skin effect and proximity effect. High-frequency welding uses these two effects to weld steel pipes. These two effects are used to realize metal The basics of high frequency welding.
About HFW

High-frequency welding uses the skin effect to concentrate the energy of high-frequency current on the surface of the workpiece; and uses the proximity effect to control the location and range of the high-frequency current flow path. The speed of the current is very fast, it can heat and melt the edge of the adjacent steel plates in a very short time, and realize the butt joint by extrusion. Each has its own advantages and disadvantages. Generally, the specific choice should be analyzed on a case-by-case basis.