EFW is Electric Fusion Welding, a welding process without filler.

Also, EFW (Electric Fusion Welded) Pipe in terms of ferrous material specifications under ASME implies filler metal added (SA-691 and SA-671).

There are three processes for metallic pipe manufacture. Seamless (SMLS) Pipe is formed by drawing a solid billet over a piercing rod to create the hollow shell.

Seamless Pipe provides the most reliable pressure retaining characteristics, and is often more easily available than welded pipe.

Welded, Electric Resistance Welded (ERW) and Electric Fusion Welded (EFW) Pipe is formed by rolling plate and welding the seam. The weld flash can be removed from the outside or inside surfaces using a scarfing blade. The weld zone can also be heat treated, so the seam is less visible.

Welded Pipe often has tighter dimensional tolerances than seamless, and can be cheaper if manufactured in the same quantities. Large diameter Pipe (about 10 inches or greater) may be ERW, EFW or Submerged Arc Welded (SAW) Pipe.