Why tube
Torsional stiffness. A closed section resists twist far better than an open one. On a cantilevered canopy, a curved frame or anything loaded off its axis, this frequently governs the design.
Buckling resistance. A hollow section has the same radius of gyration in both directions, so a tube column is efficient where an I-section would need bracing about its weak axis.
Appearance. This is the reason most of our tube work exists. Exposed, a tube reads as a clean line from every angle. An I-beam reads as flanges and a web, and looks different depending where you stand.
Profiling the joints
The defining skill in tube fabrication.
Where one tube meets another, the end has to be cut to the curve of the intersection — a saddle cut — so the two fit closely before welding. Done properly, the members appear to grow into each other.
The alternatives are visible compromises: flattening the tube end, notching it crudely, or leaving a gap filled with weld. All three are weaker and all three look wrong on exposed work.
Profiling is why tube joints take longer to prepare than open-section connections, and why welding quality matters more — the weld is usually visible.
Internal corrosion
The failure mode specific to hollow sections, and the one people forget.
If water gets inside a tube and cannot get out, it corrodes the section from the inside where nobody can inspect it. In coastal Mumbai, with driven monsoon rain, this happens readily.
Two valid approaches:
Seal it completely. Ends capped and welded, so nothing enters. Requires that no penetration anywhere lets water in.
Vent and drain it deliberately. Holes positioned so water that enters can leave, and air can circulate. Essential if the section is to be galvanised, since the bath needs to fill and drain.
What is not valid is leaving open ends and hoping. See steel fabrication for how protection is specified.
Bending
Tube can be rolled to a curve, or induction bent for tighter radii and larger sections.
The constraint is the minimum radius achievable without distorting or wrinkling the section. That figure depends on the diameter and wall thickness, and it has to be established before the geometry is finalised — a curve drawn without reference to it may simply not be makeable in that section.
Where we use it
Entrance canopies and porte-cochères, support structures for glazed roofs, atrium and structural glazing support frames, balustrade posts and handrails, and exposed architectural frames generally.
See the full structural fabrication range for how tube work fits alongside plate and open-section fabrication.