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 withstands pressure better than other types, and is often more easily available than welded pipe. Welded (also 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 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 (SAW) pipe. Cast pipe is no longer very common, but is still manufactured. Pipe is sometimes cast in a centrifuge.
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