Difference Between Seamless and Welded Pipe?

Seamless (SMLS) pipe is formed by drawing a solid billet over a piercing rod to create the hollow shell. Seamless pipe withstands pressure better than other types, and is often more easily available than welded pipe.

Welded 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 to make the seam less visible.

Welded pipe often has tighter dimensional tolerances than seamless, and can be cheaper if manufactured in the same quantities. Large-diameter pipe (25 centimetres (10 in) or greater) may be ERW, EFW or Submerged Arc Welded pipe.

The difference in the basic manufacturing method is obvious from the names. Seamless pipe is extruded and drawn from a billet while welded pipe is produced from a strip that is roll formed and welded to produce a pipe. Welded pipe is considerably less expensive than seamless pipe and is readily available in long continuous lengths.

VS.	Seamless	Welded
Manufacturing method	extruded and drawn from a billet	roll formed and welded to produce a pipe
Cost	Expensive	Less expensive
Size		diameter Larger and longer
Pressure	withstands pressure better

The basis for much of today’s bias regarding seamless vs. welded piping probably stems from early manufacturing processes when the weld area was not reworked to provide a homogeneous pipe wall. Even today the standard for working the weld area is very open allowing great variance in the final product. Seamless piping simply avoids the potential for any defect in the corrosion resistance of the weld area.

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