CHS 323.9×12.5 vs PIPE 12XS
CHS 323.9×12.5 is an CHS Hot-finished section from the UK Blue Book (SCI P363); PIPE 12XS is the closest equivalent in the American AISC Shapes Database. CHS 323.9×12.5 carries more bending: 1210 cm³ of plastic modulus against 1150.4 cm³, 5.2% more. They weigh essentially the same, 96 kg/m and 97.5 kg/m. Both are about 324 mm deep, so either fits the same construction zone.
| Property | CHS 323.9×12.5 CHS Hot-finished | PIPE 12XS Pipe | Difference |
|---|---|---|---|
| Mass | 96 kg/m | 97.5 kg/m | -1.5% |
| Depth | 323.9 mm | 323.8 mm | same |
| Width | 323.9 mm | 323.8 mm | same |
| Web thickness | 0 mm | 11.8 mm | -100.0% |
| Flange thickness | 0 mm | 0 mm | same |
| Area | 122 cm² | 112.9 cm² | +8.1% |
| Second moment, major (Iy) | 14,800 cm⁴ | 14,110 cm⁴ | +4.9% |
| Plastic modulus, major (Wpl,y) | 1,210 cm³ | 1,150.4 cm³ | +5.2% |
| Elastic modulus, major (Wel,y) | 917 cm³ | 871.79 cm³ | +5.2% |
| Second moment, minor (Iz) | 14,800 cm⁴ | 14,110 cm⁴ | +4.9% |
| Plastic modulus, minor (Wpl,z) | 1,210 cm³ | 1,150.4 cm³ | +5.2% |
| Radius of gyration, minor (iz) | 11 cm | 11.05 cm | -0.5% |
| Torsion constant (It) | 29,700 cm⁴ | 28,220 cm⁴ | +5.2% |
CHS 323.9×12.5 to BS EN 10210-2:2006; PIPE 12XS to AISC Shapes Database v16.0. Difference is expressed relative to PIPE 12XS.
How to choose between them
On stiffness, CHS 323.9×12.5 has the larger second moment of area: 14,800 cm⁴ against 14,110 cm⁴, a difference of 4.9%. This matters more often than the strength comparison, because on normal floor spans deflection rather than bending capacity sets the beam size - so if the two are close on modulus but apart on inertia, the stiffer one is usually the better answer even when it is not the stronger one.
Measured as bending capacity per kilogram of steel, CHS 323.9×12.5 is the more efficient section: 12.6 against 11.8 cm³ per kg/m, 6.8% better. Over a floor of repeated beams that difference is real tonnage, though it is often outweighed by whichever section the fabricator can actually source.
These come from different catalogues, so treat the swap as a design change rather than a like-for-like substitution. CHS Hot-finished sections are specified to BS EN 10210-2:2006 and Pipe to AISC Shapes Database v16.0; the steel grades, tolerances and available lengths differ, connection details and bolt gauges are set out differently, and the two are rarely both stocked in the same market. Check availability before changing a section on a drawing to save a marginal amount of weight.
In short, CHS 323.9×12.5 is the stronger section and CHS 323.9×12.5 is the lighter one; where those are the same section, it is the clear choice, and where they are not, decide on whether your design is governed by capacity or by tonnage.