What Is EFW Pipe?

EFW (Electric Fusion Welded) pipe is manufactured by forming steel plate into a cylindrical shape and joining the edges with an electric fusion welding process that uses filler metal. Unlike ERW/HFW, which rely on pressure welding without filler, EFW adds weld metal to fill the joint. The most common EFW method is submerged arc welding (SAW), but other processes like GMAW or SMAW may also be used.

EFW pipes are covered primarily by ASTM A671 (for atmospheric and lower temperatures) and ASTM A672 (for high-pressure service at moderate temperatures).

Property	EFW Pipe
Weld type	Longitudinal, with filler metal
Welding process	SAW, GMAW, or other fusion processes
Base plate specs	ASTM A285, A515, A516, A537
Pipe specs	ASTM A671, ASTM A672, ASTM A691
Size range	NPS 4 to NPS 60+
Wall thickness	6 mm to 50+ mm
Pressure classes	ASTM A672 Classes 10-72 (increasing test requirements)
NDT	RT and/or UT on weld seam; hydrostatic test
Joint factor (E)	0.85-1.0 depending on examination level

ASTM A671 vs A672 vs A691

Specification	Service	Temperature	Typical Grades
ASTM A671	Atmospheric and lower temperatures	Down to -46°C	CB60, CB65, CB70 (from A516 plate)
ASTM A672	High-pressure service, moderate temperatures	-29°C to 343°C	B60, B65, B70, C60, C65, C70
ASTM A691	High-pressure, high-temperature service	Up to 593°C	1CR, 1.25CR, 2.25CR, 5CR, 9CR (alloy)

The class suffix (e.g., Class 22, 32, 42) indicates the level of testing and heat treatment. Higher classes require radiographic examination and post-weld heat treatment (PWHT).

EFW vs ERW

The key differences:

• Filler metal: EFW uses it; ERW does not
• Wall thickness: EFW handles much heavier walls (50 mm+)
• Diameter: EFW starts where ERW ends (NPS 16-24 and above)
• Heat treatment: EFW can be PWHT’d; ERW typically is not
• Cost: EFW is more expensive per meter due to slower production and filler metal consumption

Pro Tip

When specifying EFW pipe per ASTM A672, always state the class explicitly. Class 12 (no RT) and Class 22 (spot RT) are not equivalent in weld quality assurance. For critical process piping, Class 32 or higher (100% RT + PWHT) is standard practice.

Applications

• Large-diameter process piping in refineries and petrochemical plants
• Penstock and water conveyance systems
• High-pressure steam lines (ASTM A691 for chrome-moly alloys)
• Pipeline headers and manifolds
• Applications where seamless pipe is unavailable in the required size

EFW pipe fills the gap between ERW (limited in wall thickness and diameter) and seamless (limited in large diameters). For pipeline-specific applications, LSAW pipe per API 5L is more common.

Read the full guide to pipe types