Technical guide

How to choose wall thickness for square tube

Wall thickness drives weight, cost, weldability and coating quality. Most buyers pick it from a previous project, which is why over-specified tube is common. Here is the decision order we use when quoting.

Start from the failure mode, not the number

Ask what actually breaks the part:

In most frames, deflection governs. Doubling the wall roughly doubles stiffness; increasing the section from 100×100 to 150×150 multiplies it by about 5 while adding less weight. Bigger section beats thicker wall for stiffness per kilo.

Manufacturing limits

Every size has a practical wall band — below it the tube ovalises, above it the corner radius grows and the mill needs a bigger coil:

• 30×30 – 50×50 mm: 1.5–5.0 mm
• 80×80 – 130×130 mm: 2.5–10 mm
• 150×150 – 200×200 mm: 5–12 mm
• 300×300 – 400×400 mm: 8–16 mm

The full matrix with weights is on the catalogue page.

Thin wall: cheaper steel, more process cost

Below about 2 mm, welding becomes the cost driver: burn-through, distortion and fit-up tolerance all get worse. If the part is welded, 2.5–3 mm is usually the practical floor even when the drawing allows 1.5 mm. If it is only drilled and bolted, thin wall is fine.

Thick wall: watch the galvanising

Hot-dip galvanising needs vent and drain holes and a wall thick enough to survive the zinc bath without distortion — generally ≥ 3 mm for long hollow sections. Above 6 mm, zinc adhesion is fine but the bath time and the risk of warping on long lengths go up; we design the jig and the holes at quotation stage.

A quick checklist for your RFQ

1. Section and wall, e.g. 200×200×8
2. Grade and impact class, e.g. Q355D
3. Standard, e.g. EN 10219 or GB/T 6728
4. Length: 6 / 9 / 12 m or cut list
5. Coating: hot-dip Zn µm, or paint system
6. Any machining: holes, notches, mitres

Send those six lines and the quote comes back within 48 hours with weight, price per tonne and lead time.

FAQ

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