Welded pipe: Hot rolled or cold-rolled steel strip is formed by high-frequency induction welding (ERW) or submerged arc welding (SAW), and the weld is subjected to online heat treatment to relieve stress.
Seamless pipe: piercing round billet (oblique rolling/extrusion) → rolling pipe (continuous rolling pipe mill/three roll rolling pipe) → sizing → cold drawing (precision pipe), achieving high strength without welding seams.