Differences between ERW steel pipe and HFW steel pipe.

The differences of the ERW, HFW welding processes.

ERW welding process refers the heat generated by the resistance to current flow that pass through the jointed metals. So a large current is needed to electrify the whole surface of the steel plate or coil to the length of welding. In the ERW welding process, the electric current that pass through the entire conductor is at 50/60 Hz.

HFW welding process is not the same case with the high-frequency process, since it’s only a section of the steel metals is heated by the induction of electric coil. High-frequency is generated by either AC or DC current. In these cases, the constant current welding generator and constant voltage high-frequency welding generator are used.

Constant current welding machine generates power in 100-800 kHz. In the elder processes, the conversion of 60 Hz, AC current to HF was done by using triode and tank circuits. New welding machine uses metal oxide silicon, filed-effect transistors, usually associated with parallel resonant circuit. The constant voltage version generators use insulated gate bipolar transistors designed to power about 2000 kW with frequency rages of 100-600 KHz.

HFW is required in API 5L PSL2 ERW steel pipe

According the API 5L and ISO 3183 specification, for PSL 2 pipes in welded process the HFW welding is a mandatory requirements for ERW steel pipes. As it is an improvement from the inherent problems of hardness, lack of fusion and susceptibility of stress corrosion cracking (SCC).

ERW steel pipe includes HFW steel pipe

ERW is general designation of resistance welded steel pipes. It can be sorted into two types: alternated current welding (AC) and direct current welding (DC). According to different frequency, AC welding can be divided into low frequency welding, intermediate frequency welding, ultra frequency welding and high frequency welding. The high frequency welding (HFW) is mainly used in ordinary or thin wall steel pipe. It includes contact welding and induction welding. Direct current welding is generally used for small caliber steel tubes. In general, HFW is one of ERW production methods, it adopts the high frequency welding process. So, ERW steel pipe includes HFW steel pipe.