Hot-rolled (extruded seamless steel pipe): Round billet → heating → piercing → three-roll skew rolling, continuous rolling or extrusion → tube removal → sizing (or reduction) → cooling → billet tube → straightening → hydrostatic test (or flaw detection) → marking → warehousing.
Cold-drawn (rolled) seamless steel pipe: Round billet → heating → piercing → heading → annealing → pickling → oiling (copper plating) → multi-pass cold drawing (cold rolling) → billet tube → heat treatment → straightening → hydrostatic test (flaw detection) → marking → warehousing.