CHS 168.3×6.3 vs PIPE 6STD
CHS 168.3×6.3 is an CHS Hot-finished section from the UK Blue Book (SCI P363); PIPE 6STD is the closest equivalent in the American AISC Shapes Database. PIPE 6STD carries more bending: 173.7 cm³ of plastic modulus against 165 cm³, 5.0% more. CHS 168.3×6.3 is the lighter of the two at 25.2 kg/m against 28.3 kg/m, a saving of 11.0% on steel weight. Both are about 168 mm deep, so either fits the same construction zone.
| Property | CHS 168.3×6.3 CHS Hot-finished | PIPE 6STD Pipe | Difference |
|---|---|---|---|
| Mass | 25.2 kg/m | 28.3 kg/m | -11.0% |
| Depth | 168.3 mm | 168.3 mm | same |
| Width | 168.3 mm | 168.3 mm | same |
| Web thickness | 0 mm | 6.6 mm | -100.0% |
| Flange thickness | 0 mm | 0 mm | same |
| Area | 32.1 cm² | 33.5 cm² | -4.2% |
| Second moment, major (Iy) | 1,050 cm⁴ | 1,103 cm⁴ | -4.8% |
| Plastic modulus, major (Wpl,y) | 165 cm³ | 173.7 cm³ | -5.0% |
| Elastic modulus, major (Wel,y) | 125 cm³ | 130.93 cm³ | -4.5% |
| Second moment, minor (Iz) | 1,050 cm⁴ | 1,103 cm⁴ | -4.8% |
| Plastic modulus, minor (Wpl,z) | 165 cm³ | 173.7 cm³ | -5.0% |
| Radius of gyration, minor (iz) | 5.73 cm | 5.72 cm | +0.2% |
| Torsion constant (It) | 2,110 cm⁴ | 2,202 cm⁴ | -4.2% |
CHS 168.3×6.3 to BS EN 10210-2:2006; PIPE 6STD to AISC Shapes Database v16.0. Difference is expressed relative to PIPE 6STD.
How to choose between them
On stiffness, PIPE 6STD has the larger second moment of area: 1,103 cm⁴ against 1,050 cm⁴, a difference of 4.8%. 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 168.3×6.3 is the more efficient section: 6.5 against 6.1 cm³ per kg/m, 6.7% 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 11.0% weight.
In short, PIPE 6STD is the stronger section and CHS 168.3×6.3 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.