How A500 tubing is made

Welded A500 tubing starts as flat-rolled carbon steel coil. The strip is slit to width, cold-formed into a round through a series of forming rolls, and electric-resistance welded along the longitudinal seam — welded across the full thickness so the structural design strength of the section is assured. The welded round is then sized to final dimension, or driven through shaping stands that reform it into a square or rectangle, before cutoff.

Seamless A500 product is permitted by the specification and follows a different route (pierced and rolled rather than formed and welded), but the overwhelming majority of commercial HSS is welded.

Each step below is qualitative and producer practice varies. The point of understanding the sequence is knowing where dimensional character, weld-zone behavior, and surface condition come from — and therefore which questions to ask a producer.

• Steelmaking: open-hearth, basic-oxygen, or electric-furnace melting, with chemistry limits per grade
• Slitting: coil is slit to the exact strip width the finished periphery requires
• Forming: progressive rolls bend the strip into an open round
• ERW welding: the longitudinal butt joint is forged by resistance heating and pressure — no filler metal
• Flash removal: the outside weld bead is trimmed; inside bead practice varies by product
• Sizing / shaping: rolls bring the round to final size, or reform it into square or rectangular section
• Cutoff, testing, inspection: tension and flattening tests, dimensional checks, and marking

Cold forming work-hardens the section non-uniformly — most severely at the corners of squares and rectangles. This is why corner regions of shaped HSS have elevated strength and reduced ductility relative to the flats, a behavior that structural design standards and welding procedures account for. It is also part of why Grade D's heat-treatment requirement exists as a distinct product within the family.

The specification requires tension testing and flattening testing, inspection at the place of manufacture, and a workmanlike finish free from defects. Certification documents what was measured; if your project needs specific test frequencies, supplementary requirements, or witnessed inspection, those belong on the purchase order.