Part 1: fabrication of ventilation, smoke-control and air-conditioning ducts
To raise transport efficiency, cut waste and protect finished parts, we prefabricate in the workshop and assemble on site: machine-formed semi-finished parts are moved to site for final assembly.
Duct material and joint method
| Item | System | Sheet | Joint |
| 1 | Supply, fresh-air and exhaust ducts (round diameter or rectangular long side) | ≤200: δ=0.5 galvanised steel >200–500: δ=0.75 galvanised steel >500–1120: δ=1.2 galvanised steel | Flanged |
| >1120 | δ=2.0 mild steel | Welded | - |
| 2 | Duct through fire wall | ≥200–500: δ=1.0 galvanised steel >500–2000: δ=1.2 galvanised steel | Flanged |
| 3 | Ventilation duct embedded in concrete | Welded steel pipe | Welded |
| 4 | Fire smoke exhaust duct | δ=1.6–2.0, mild steel | Welded or flanged |
3. A metal rectangular duct with side >630 mm, or an insulated duct with side >800 mm, and with length >1250 mm, or a low-pressure duct with single flat area >1.2 m², or medium/high-pressure >1.0 m², needs stiffening.
4. If a stiffening plate is added inside the duct, its thickness matches the duct. A branch meets the main at a tee; when the branch is within 150 mm of the main top or bottom, make an arc tee; beyond 150 mm, use an inserted tee with a tight joint.
5. Duct elbows follow standard drawing 91SB6. Flexible joints for AC and ventilation may use canvas; smoke systems need non-combustible flexible material.
6. For a metal rectangular duct joined to an angle-steel flange, with wall ≤1.5 mm use flanged riveting with firm rivets; with wall >1.5 mm use full welding or intermittent flange welding. Secure the flange with galvanised rivets; before riveting, derust and apply two coats of red-lead primer. The duct bite must be tight, flat and burr-free.
7. The angle-steel flange joint suits high-pressure ventilation (smoke-control and super-quiet systems).
Angle-steel flange material for rectangular ducts
| Duct long side (mm) | Flange section (angle steel) |
| ≤630 | 25×3 |
| 630–1500 | 30×3 |
| 1500–2500 | 40×4 |
| 2500–4000 | 50×5 |
8. Rectangular elbow guide vanes
(1) An air-conditioning duct with rectangular long side >500 mm at a right-angle elbow needs guide vanes. The vane radius matches the elbow angle. A short-radius rectangular elbow needs guide vanes; vane thickness equals the duct wall thickness.