Difference between ERW pipe and HFW pipe

ERW pipe is the abbreviation of electric resistance welded pipe and HFW pipe stands for high frequency welded steel pipe. The pipe is made of steel coils with welds running parallel to the pipe. It is one of the most versatile tools in agricultural, industrial and construction activities. The manufacturing process of ERW steel pipes includes HFW. ERW welding includes low, medium and high frequency welding, while HFW is particularly suitable for high frequency resistance welding.

The difference between ERW pipe and HFW pipe:

1. Working principle
ERW (Electric Resistance Welding)‌, is a method of welding by applying pressure through electrodes and using resistance heat generated by current passing through the contact surface of the joint and adjacent areas. This method is suitable for straight seam resistance welded pipes, including ERW and HFW.
 

HFW (High Frequency Welding), that is, high frequency welding, uses the skin effect and proximity effect generated when high-frequency current passes through metal conductors for welding. These two effects are the basis for realizing high-frequency welding of metals. 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 position and range of the high-frequency current flow path. This method is characterized by fast current speed and high production efficiency. It can heat and melt the edges of adjacent steel plates in a short time, and achieve docking through extrusion.

2. Production efficiency
ERW pipe is a steel pipe welded using the principle of resistance heating. The welding speed is slow and the production efficiency is average. In the ERW welding process, the current through the entire conductor is 50/60 Hz.

HFW pipe is a steel pipe welded using the principle of high-frequency induction heating. It has fast welding speed and high production efficiency. High frequencies are generated by alternating or direct current. In these cases, constant current welding generators and constant voltage high frequency welding generators are used.

Constant current welding machines produce power from 100-800 kHz. In earlier processes, conversion of 60 Hz AC current to high frequency was accomplished through the use of transistors and energy storage circuits. Newer welders use metal oxide silicon, field effect transistors, often associated with parallel resonant circuits. The constant voltage version of the generator uses insulated gate bipolar transistors and is designed for a power of approximately 2000 kW and a frequency range of 100-600 KHz.

Compared with 60 Hz line current, high-frequency current has two obvious characteristics:
The 60Hz power frequency current flows through the entire conductor, while the high-frequency current only flows through the surface of the conductor, so there is a "skin effect".
When two conductors carrying high-frequency current are placed close to each other, the current is concentrated on the two adjacent surfaces of the conductor, which is the "proximity effect".

3. Weld quality
The weld quality of HFW steel pipe is high, and the welding strength and sealing are good.
The weld quality of ERW steel pipes is average, and the welding strength and sealing performance are slightly inferior to HFW steel pipes.

4. Scope of application
ERW steel pipes are suitable for piping systems in general engineering structures, hydraulic supports and other fields.
HFW steel pipes are suitable for oil and gas transportation, oil well pipelines, building structures and various types of mechanical pipes. However, the quality of HFW steel pipes is affected by many factors such as raw materials and technology. And production quality control becomes difficult. Therefore, the yield rate and welding process still need to be continuously improved.

The connection between ERW and HFW:

ERW steel pipes include HFW steel pipes.

ERW is the general name for electric resistance welded steel pipes. It can be divided into two types: alternating current welding (AC) and direct current welding (DC). According to different frequencies, AC welding can be divided into low-frequency welding, medium-frequency welding, ultra-high-frequency welding and high-frequency welding. High frequency welding (HFW) is mainly used for ordinary or thin-walled steel pipes. It includes contact welding and induction welding. Small-diameter steel pipes are generally welded by direct current. Generally speaking, HFW is one of the ERW production methods, which uses high-frequency welding process. Therefore, ERW steel pipes include HFW steel pipes.

Tips: ASTM A53 Gr.B is the grade in ERW high frequency welded pipe, divided into A and B grades. ASTM is only a set of specifications. ASTM steel pipe A53 A corresponds to the Chinese standard GB8163 raw material is 10# steel, and A53 B corresponds to the Chinese standard GB8163 raw material 20#.
For example: ASTM (standard) A53 (grade) gr (abbreviation of grade) b (grade B)

Read more: Matters needing attention when purchasing welded steel pipes

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