ERW Welded Pipe is formed by rolling plate and welding the seam by high frequency welder. The weld flash can be removed from the outside or inside surfaces using a scarfing blade. The weld zone of ERW carbon steel pipe can also be heat treated to make the seam less visible. There are round ERW steel pipe and square ERW welded pipe and triangle ERW carbon welded pipe.

Seamless steel (SMLS) pipe refers to pipe without a welded seam, produced by a hot-forming process, which can be followed by cold sizing or cold finishing to produce the desired shape, dimensions and properties. (according to API 5L Spec.)
seamless pipes 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.