Hollow sections look interchangeable on a drawing, and that is where problems start. A 200×100×8 rectangular tube can be hot-finished or cold-formed, made to a European or an American standard, with different corner radii, different thickness tolerances and different assumptions in the design calculation. Any of those can surface later as a connection plate that will not seat, a member that is lighter than the model assumed, or an assembly that arrives at the galvanizer sealed shut. Each is avoidable if the carbon steel hollow sections order carries the right information before cutting begins.
This guide covers square (SHS), rectangular (RHS) and circular (CHS) sections, called HSS in North America. It compares the main product standards, shows which design assumptions follow from the choice, and lists the checks that belong in the purchase order, the cutting plan and the galvanizing details.
Key takeaways
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Begin with the approved structural requirement
SHS, RHS and CHS name the shape. They say nothing about grade, standard, manufacturing process or resistance in a particular structure. Take the section designation, grade, wall thickness, product standard and manufacturing condition from the design documents, and state the orientation where it matters for connections. A substitution that looks equal on outside dimensions can change member behaviour, connection detailing and fabrication, so any proposed change goes to the responsible engineer.
Give suppliers the full requirement when you request quotations for carbon steel hollow box. “50×50 square tube, 6 m” leaves out grade, wall, standard, tolerance class, surface condition, testing and traceability, and a quotation against that description is not technically complete. Raise missing information on the drawings before accepting any offer.
Compare the product standards: what actually differs
The main choice is between European and American specifications and, within the European ones, between hot-finished and cold-formed production. A summary of the verified points:
| EN 10210 (hot-finished) | EN 10219 (cold-formed) | ASTM A500 / A1085 | |
| Production | Hot-finished, or normalized after forming | Formed cold from strip and welded | Both cold-formed; A500 welded or seamless, A1085 welded |
| Typical grades | S235JRH to S355J2H and S355K2H; N and NL grades S275NH, S355NH, S275NLH, S355NLH | S235JRH to S355J2H; S275NH; plus higher strength S420MH, S460MH, S500MC, S700MC | A500 Grade C: 50 ksi yield, 62 ksi tensile. A1085: 50 ksi minimum yield, 70 ksi maximum |
| Wall thickness range (square) | 5 to 16 mm | 1.5 to 14.2 mm | Walls up to 1 in nominal; maximum perimeter 88 in |
| Size limit (round, OD) | Up to 406.4 mm | Up to 406.4 mm | A500 within 88 in perimeter |
| Design point | Check its own corner and tolerance requirements | Check its own corner and tolerance requirements | A500: design at 0.93 t. A1085: full nominal t |
Several practical points follow. S355J2H is produced in both EN standards, but only EN 10210 covers S355K2H and the higher-toughness N and NL grades, while only EN 10219 covers the higher-strength S420MH to S700MC range. Equal grade names therefore do not mean equal products, and equal yield strength does not mean equal toughness, tolerance or corner geometry. The data above is drawn from ArcelorMittal’s hollow structural section range and the Steel Tube Institute’s guide to HSS specifications; confirm ranges for the specific mill and size before relying on them.
The difference between EN 10219 and EN 10210 is explained in more detail in this review of EN 10210 and EN 10219 hollow section differences. Whether a substitution is acceptable is a design decision. Ask the supplier to flag any departure from the requested standard or condition in writing, so it is reviewed before cutting rather than discovered afterwards.
| Why A500 members are designed at 0.93 of nominal thickness
ASTM A500 permits a wall thickness tolerance of 10%. To allow for this, AISC 360 requires HSS design calculations to use 0.93 times the nominal thickness. ASTM A1085 has a tighter thickness tolerance (minimum -5%) and a minimum mass tolerance of -3.5%, so AISC allows design at full nominal thickness. A1085 also specifies minimum Charpy toughness (25 ft-lb at 40 °F). The trade-off is availability: A1085 is typically produced on demand rather than stocked, so check lead time before specifying it. This is why “equivalent” sections cannot be swapped without checking the design basis. |
Check hollow section tolerances against the planned connections
Outside dimensions are only one of the characteristics that govern fit-up. The Steel Tube Institute’s HSS tolerance guide, which ASTM has approved as the standard guide for measuring HSS tolerances, covers outside dimensions, wall thickness, length, straightness, squareness of sides, corner radius and twist. Each of those can affect a joint:
- Corner radius: A500 limits the outer corner radius to a maximum of 3t, and design practice treats the flat width as starting about 2.25t from the corner. An internal plate or insert sized to the nominal internal width can clash with the inside corner.
- Squareness and twist: These determine whether end plates and gussets seat flat, and whether a long member lines up at both ends.
- Straightness: This matters for long columns and trusses, where bow adds to out-of-plumb and load eccentricity.
- Wall thickness and weld seam: Seam position and internal weld bead can interfere with sleeve inserts and internal stiffeners. If seam position matters to an operation, ask what can be controlled and documented rather than assume an orientation.
Name the contractual standard and edition, the characteristic and the measuring method. Shop drawing tolerances do not change supply tolerance. If the fabrication really needs a tighter limit than the product standard allows, discuss feasibility, measurement and acceptance with the supplier before the order is placed, and expect it may carry a cost or a restricted source.
Order lengths with the cutting and identification plan
Stock lengths are set by mill and transport, and are not necessarily the best lengths for your cutting plan. Compare finished lengths, saw kerf and end preparation allowances and handling limits before confirming supply length. A length that leaves a 300 mm offcut on every member produces scrap you pay for. A cut list that nests pieces from a few well-chosen lengths often costs less than ordering to the nearest standard length.
Traceability is lost at the saw. Paint or stencil markings are cut away with the end of the tube, and an unmarked offcut next to a certificate is not a material link. If the project needs traceability, agree how identity is transferred to each cut piece before the first cut, whether by hard-stamping, paint marking or tagging, and who verifies it. For mixed orders, keep section designations, drawing references and bundle identification aligned, so receiving staff can match bundles to members and phases without having to recognise a section by eye.
Plan galvanizing and surface treatment before closing the assembly
State whether sections will be supplied bare, shop-primed, painted, galvanized, or prepared for treatment after fabrication. For hot-dip galvanizing after fabrication, the main issue is that a hollow fabrication is lowered into cleaning solutions and molten zinc and lifted out again. Air must escape and liquids must flow in and drain out.
The American Galvanizers Association explains that required vent and drain holes in hollow structural sections serve two purposes: letting the part fill and drain completely, and preventing damage. Cleaning solutions or water trapped in a sealed or overlapped cavity flash to steam when the part meets molten zinc, and the AGA notes the resulting pressure can rupture the fabrication.
Because parts are dipped at an angle, vent holes belong at the highest point and drain holes at the lowest point of each enclosed section as it hangs in the kettle, and the AGA recommends that venting is visible from the outside so the galvanizer can verify it. Venting for square and rectangular sections needs separate attention: the internal corners trap air at the high point and liquid at the low point, so the AGA states that substitute details developed for round tube with a base plate should not be assumed adequate for SHS and RHS.
Where fully open ends are not possible, it describes two-hole and four-hole corner designs, with the four-hole design preferred for finish and for flexibility in how the part is oriented for lifting.
Put the agreed openings on the shop drawings, have them reviewed by the engineer, and agree with the galvanizer whether holes will be left open or plugged afterwards, since zinc or aluminium plugs are commonly used where holes must be hidden. Also decide in advance how the finished fabrication will be inspected and accepted.
Make receiving acceptance a usable record
Material is checked at receiving before it is released to fabrication: identification against the order, quantity, dimensions, condition and certificates for the supplied heat. Recording deviations at this point is far cheaper than finding them after welding. A compact checklist keeps responsibilities visible:
| Item | Confirm before ordering | Check before fabrication release |
| Structural specification | Section, grade, standard, manufacturing route and design thickness basis | Product markings and certificate correspondence |
| Fabrication geometry | Corner radius, squareness, straightness, twist and any additional controls | Agreed measurements and approved deviations |
| Length and allocation | Cutting plan, offcut use and identification transfer method | Correct lengths, bundles and traceability |
| Surface treatment | Treatment route, vent and drain details, galvanizer agreement | Condition and readiness for the next operation |
Common mistakes when ordering hollow sections
- Ordering by outside dimensions and length only, and discovering later that grade, standard or wall differ from the design.
- Treating EN 10210 and EN 10219 products, or A500 and A1085 products, as interchangeable because the yield strength matches.
- Designing connection plates to nominal internal dimensions without allowing for corner radius.
- Reusing round-tube vent hole details on rectangular or square assemblies.
- Sending a sealed assembly for galvanizing, assuming the galvanizer will add vent holes.
| Sample line item for a hollow section order
“RHS 200×100×8, grade [x], to [standard and edition], [hot-finished / cold-formed], length [x] m cut to list, tolerances per [standard], mill certificate to [type] linked to heat number, identification transfer required on cut pieces, surface: [bare / galvanized after fabrication].” Fill in the bracketed items from the design documents and keep one line per section size. |
Frequently asked questions
What is the difference between SHS, RHS, CHS and HSS?
SHS, RHS and CHS describe square, rectangular and circular hollow sections. HSS is the term used mainly in North America for hollow structural sections. These labels describe the shape, not the grade, standard or structural resistance.
What is the difference between EN 10210 and EN 10219?
EN 10210 covers hot-finished structural hollow sections, and EN 10219 covers cold-formed welded ones. They overlap in several grades such as S355J2H, but each has its own tolerances and grade range, so the distinction must be carried into the purchase order.
Is ASTM A500 the same as EN 10219?
No. Both are cold-formed products, but they are separate specifications with different grades, tolerances and design conventions. For example, A500 members are designed at 0.93 times nominal thickness under AISC 360.
Why is ASTM A1085 specified instead of A500?
A1085 has a tighter thickness and mass tolerance, so members can be designed at full nominal thickness, and it specifies minimum Charpy toughness. It is generally produced on demand rather than stocked, so lead time should be checked.
Does a shop drawing change the supply tolerance of the material?
No. If fabrication needs tighter limits than the product standard provides, agree feasibility, measurement and acceptance with the supplier before ordering.
Why do hollow sections need vent and drain holes before hot-dip galvanizing?
Air must escape so the part fills with cleaning solution and zinc, and liquids must drain out. Trapped moisture can flash to steam on contact with molten zinc and damage the part. Vent holes go at the high point and drain holes at the low point as the part hangs in the kettle.
