General classification of seamless square tubes

(a) Classified by process - arc welded pipe, resistance welded pipe (high frequency, low frequency), gas welded pipe, furnace welded pipe
(b) Classified by weld seam - straight seam welded pipe, spiral welded pipe
2. Classification by section shape
3. Classification by wall thickness - thin-walled steel pipes, thick walled steel pipes
4. Classified by purpose - steel pipes for thermal equipment, mechanical industry, petroleum, geological drilling, container, chemical industry, special purpose, and others