The dividing criterion is external diameter: pipes with an external diameter exceeding 406.4 mm (16 inches) fall under 7305, while smaller-diameter welded pipes and hollow profiles classify under 7306. Both headings further subdivide by welding method and end use.

Yes. For line pipe, the schedule distinguishes longitudinally submerged-arc-welded pipe (730511) from other longitudinally welded pipe (730512) and from riveted or similarly closed pipe (730519). For other tubes and pipes, longitudinally welded (730531) is separated from non-longitudinally welded (730539). Importers should confirm the welding process used in production to select the correct subheading.