Difference between ERW Pipe and EFW Pipe

When selecting the right type of welded steel pipe for your project, understanding the difference between ERW pipe and EFW pipe is crucial. These two types of pipes may appear similar on the surface, but they differ significantly in manufacturing processes, welding techniques, performance characteristics, and applications.

What Is ERW Pipe?

ERW stands for Electric Resistance Welding. This type of pipe is made by cold-forming a flat steel strip into a round shape. The edges are then heated using high-frequency electrical current and fused together through pressure from rollers. Notably, no filler metal is used in this process.
The key to ERW welding lies in two physical effects:
Skin effect: The high-frequency current flows along the surface of the steel.
Proximity effect: It concentrates the current near the pipe edges.
These combined effects heat the edges of the steel strip to welding temperature, and the pressure applied by squeeze rollers forms a solid-state forged weld. This welding zone can be further refined through online or offline heat treatment, improving toughness and reducing residual stress. High-quality ERW pipes often have weld strength and toughness nearly equivalent to the base metal.

EFW Pipe Meaning

Electrofusion welding (EFW steel pipe) refers to electron beam welding, which uses high-speed motion to convert the impact kinetic energy of the electron beam into heat to heat the workpiece, so that the workpiece leaves the melt and forms a weld.
It is mainly used for welding dissimilar steels, welding thin plates or metal weldments with high power density. It can be quickly heated to high temperatures and can melt any refractory metals and alloys. Deep fusion welding has a fast speed and a very small heat-affected zone, so it has little effect on the performance of the joint and there is almost no deformation of the joint. However, due to the use of X-rays for welding, special welding rooms are required.

Submerged Arc Welding (SAW) - Electric Fusion Welding (EFW) is a process that uses an electric arc to heat the metal through one or more consumable electrodes and a workpiece to create metal and filler metal. The material is completely melted and no pressure is required. The filler metal part comes entirely from the electrode. Gas Metal Shielded Welding (GMAW) - An electric fusion welding (EFW) similar to submerged arc welding, but its protection comes from an inert gas, which is more effective.

Differences Between ERW and EFW Pipes

Feature	ERW Pipe	EFW Pipe
Full Name	Electric Resistance Welding	Electric Fusion Welding
Welding Method	Pressure welding, no filler	Arc welding, uses filler material
Heat Source	High-frequency electric current	Electric arc
Shielding	None	Flux (SAW) or gas (GMAW)
Filler Material	Not used	Required
Weld Seam Toughness	Equal to base metal after treatment	Slightly lower than base metal
Common Standards	API 5L, ASTM A53, ASTM A500	ASTM A671, A672, A691
Typical Applications	Structural, water, and gas pipelines	High-pressure and high-temperature use

Quality and Inspection Considerations

For both ERW and EFW pipes, ensuring weld quality is critical. Advanced non-destructive testing (NDT) methods, including ultrasonic inspection and radiographic testing, are commonly used to evaluate weld soundness.

ERW pipe weld zones are often refined through online heat treatment, allowing the grain structure to be restored and improving overall ductility. This enables the weld zone to have properties nearly identical to the rest of the pipe.

EFW pipes, especially those using SAW techniques, rely heavily on the quality of the consumable electrodes and filler metal. Poor control over these parameters may lead to defects or inconsistent weld strength.