How RHS, SHS and CHS are manufactured

RHS, SHS and CHS describe cross-sectional shape:

• RHS — rectangular hollow section;
• SHS — square hollow section;
• CHS — circular hollow section.

They do not identify one single manufacturing process.

A critical point is:

EN 10210 does not mean “seamless”. Hot-finished EN 10210 hollow sections can be either welded or seamless.

That distinction is frequently misunderstood in steel procurement.

Route 1: cold-formed welded hollow sections

A common EN 10219 route starts from hot-rolled coil or strip.

Typical process

1. coil is uncoiled and prepared;
2. strip passes through forming rolls;
3. it is formed into a circular/open tube;
4. the longitudinal seam is welded, commonly by HFI/ERW;
5. the tube is sized;
6. for RHS/SHS it is further roll-formed into square or rectangular shape;
7. lengths are cut, straightened and inspected.

EN 10219 is specifically the European family for cold-formed welded structural hollow sections.

Cold forming influences corner geometry, residual stresses and local properties. Those effects are part of why EN 10219 and EN 10210 should not be reduced to “the same tube with different paperwork”.

Route 2: hot-finished welded hollow sections

A welded tube can also become a hot-finished structural hollow section.

One documented industrial route is:

1. hot-rolled coil is formed and HFI welded into a circular mother tube;
2. the weld seam is treated and inspected;
3. the full tube body is reheated to hot-forming temperature;
4. the hot tube is finished as CHS or reformed to RHS/SHS;
5. the section is cooled, sized and inspected.

Mannesmann publicly describes a route in which cold-finished HFI circular pipe is heated through the full body above 870°C and then processed into hot-finished circular, square and rectangular sections.

This is a clear real-world example of a welded EN 10210-type manufacturing route.

Route 3: seamless hollow sections

CHS can also be made seamlessly from pierced solid billet using seamless-pipe technology.

Seamless circular hollows may then be processed further where the producer has a qualified route for square or rectangular hot-finished sections.

Seamless manufacture removes the longitudinal weld seam, but it does not automatically make the material normalized, TMCP, or otherwise superior. Delivery condition remains a separate requirement.

See How seamless steel pipe is manufactured.

EN 10210 vs EN 10219 in manufacturing terms

The precise permitted grade, manufacturing and delivery conditions still come from the applicable standard edition and order.

For a fuller comparison, see EN 10210 vs EN 10219.

Large fabricated hollow sections

Very large RHS/SHS/CHS can fall outside continuous tube-mill ranges.

They may instead be fabricated from plate using:

• press forming;
• rolled cans;
• longitudinal seam welding;
• multiple longitudinal seams;
• circumferential welding to build longer members.

Such products should not automatically be treated as standard mill-produced EN 10210/10219 hollow sections merely because their geometry is rectangular, square or circular. The applicable product standard, execution standard, welding qualification, tolerances, NDT and certification route need to be defined explicitly.

What determines availability

A manufacturer's practical range depends on:

• coil/plate width;
• forming-line capacity;
• weld-line capability;
• hot-finishing equipment;
• section sizing stands;
• wall thickness;
• corner-radius capability;
• grade and delivery condition.

This is why a stockholder may have a size in S355J2H under one product standard but not in an offshore or higher-strength variant.

Procurement takeaway

When an RFQ says only “RHS 300 × 200 × 12.5, S355”, important information is still missing.

Clarify at least:

• EN 10210 or EN 10219?
• welded or seamless if the project restricts the route?
• hot-finished or cold-formed?
• exact grade suffix/delivery condition?
• tolerances?
• inspection document?
• impact testing/NDT?
• fixed length and cutting tolerance?

And remember: EN 10210 is not synonymous with seamless.

References and verification sources

• DIN EN 10210-1 — Hot-finished structural hollow sections
• DIN EN 10219-1 — Cold-formed welded structural hollow sections
• Mannesmann MSH® Sections — documented HFI + hot-finishing route