20# seamless steel pipe
Technological process:
Hot rolling (extruded seamless steel pipe): round tube billet, heating, perforation, three roll skew rolling, continuous rolling or extrusion, depipe, sizing (or reducing diameter), cooling, tube straightening, quality inspection wall thickness, water pressure test (or flaw detection), marking, and warehousing.
Cold drawn (rolling) seamless steel pipe: round tube billet, heating, perforation, head, annealing, acid washing, oil (copper plating), multi pass cold drawing (Leng Zha), tube of billet, heat treatment, straightening, quality inspection wall thickness, water pressure test (flaw detection), mark and warehousing.
Size standard
Deviation grade
Standardized external diameter allowable deviation
D1
+ 1.5%, minimum + 0.75 mm
D2
It is 1%. Minimum 0.50 mm
D3
Minimum + 0.30 mm of + 0.75%.
D4
It is 0.50%. Minimum 0.10 mm