Why Greenhouse Structures Are a Pipe Business
Modern commercial greenhouses — multi-span Venlo glasshouses, film tunnels, nurseries — are steel frames wearing a skin of glass or film. The frame is almost entirely roll-formed and round hollow sections: columns, arches (bows), gutters, purlins, braces and anchor posts. A hectare of multi-span greenhouse consumes roughly 20–30 tonnes of steel tube, and growers replace or extend structures every 10–20 years — which makes greenhouse tube a steady, specification-light export business for welded pipe mills, if you understand what actually matters in this market.
| Structural member | Typical section | Typical sizes |
|---|---|---|
| Columns / posts | Round hollow section, hot-dip galvanized | 60.3 × 2.0–3.0 mm, 76.1 × 2.6–3.2 mm |
| Arches (bows) | Round, pre-galvanized or HDG after bending | 25–60.3 mm OD, wall 1.5–2.6 mm |
| Gutters | Roll-formed open profile from strip (not pipe) | coil ≤ 3 mm |
| Purlins / braces / cross ties | Round, mostly pre-galvanized | 20–33.7 mm OD, wall 1.2–2.0 mm |
| Anchor / foundation posts | Round, heavy wall, hot-dip galvanized | 76.1–114.3 mm, wall 3.0–5.0 mm |
The Real Specification Is the Corrosion System
Mechanically, greenhouse loads are modest — wind, snow, crop weight. The frame rarely needs more than S235/S290-class steel. What decides the service life is the zinc:
| Coating route | How it’s done | Service expectation | Trade-offs |
|---|---|---|---|
| Pre-galvanized (continuous ZN/ZAM strip) | Tube welded from pre-coated strip; weld area bare or touched up | 10–15 yrs inland, less in humid coastal greenhouses | Cheapest, clean appearance; the welded seam is the weak point |
| Hot-dip galvanized after fabrication | Finished tubes (or bent arches) dipped per ISO 1461 / ASTM A123 | 20–30 yrs; inside the humid greenhouse too | Costs more, coating thickness ≥ ~55–85 μm typical on tube; bends must be made before or after dip by agreement |
| Zn-Al-Mg (ZAM) strip | Continuous coating with Al + Mg additions | Equal or better than HDG in tests, self-healing at cut edges | Newer, premium price, growing fast in Japanese and European projects |
In export orders the coating choice is where money is made or lost. Benders arch pre-galvanized tube after welding, and every bend plus every weld spot is bare steel. Buyers who specify hot-dip after bending get a frame that outlives the film three times over — and a price about 15–25% higher.
Standards You Will See on an Order
- Structure tube: EN 10219 (cold-formed welded hollow sections), ASTM A500 Gr B/C, or the mill’s own greenhouse spec; Chinese projects order per GB/T 6728 with steel per GB/T 700/1591.
- Water and fog lines inside the house: ordinary galvanized pipe per EN 10255 / GB/T 3091 — a natural cross-sell on the same container.
- Coating: ISO 1461 or ASTM A123 for hot-dip; EN 10240 (or supplier spec) for pre-galv/ZAM strip coatings.
- Steel grade: S235JR / S290-class equivalent; yield matters for arch spring-back consistency more than strength.
What Buyers Actually Check on Arrival
- Coating on the weld seam of pre-galv tube — the classic early-rust point; ask for the mill’s weld-zone repair statement.
- Bend quality of arches — no ovalization beyond ~5%, no coating cracks at the bend if dipped after bending.
- Wall thickness — greenhouse tube is thin-wall (1.5 mm is common), exactly where under-weight tolerance games happen. Weigh the bundle: 1.24 kg/m is the theoretical number for 33.7 × 1.5; weigh, don’t trust stencils.
- End finish and packing — thin tubes dent; plastic end caps and taped bundles in bundles of ~20–30.
Agriculture beyond greenhouses: the same product family covers livestock housing frames, vineyard and orchard trellis posts, shade-house structures and grain-drying frames — same sizes, same zinc logic, often the same customer. Quoting ‘agricultural structures’ rather than ‘greenhouses’ widens the funnel considerably.
Frequently Asked Questions
Should arches be bent before or after galvanizing?
Bending after HDG is common and standard-compliant (ISO 1461 tolerances account for it), but coating cracks at tight bends should be repaired with zinc-rich paint. Bending before dipping gives the best protection — agree the sequence in the order.
What wall thickness for film greenhouses in snowy regions?
Snow load governs the arch spacing and section; as a rule of thumb 2.0–2.6 mm walls on 48.3–60.3 mm arches with closer spacing (1.5–2 m). Local agricultural building codes rule — we quote to your drawing.
Is pre-galvanized tube acceptable for export projects?
For dry inland climates and budget projects, yes, with the weld area touched up. For humid coastal or livestock environments, specify hot-dip after fabrication.
Can you supply complete kits (arches cut, drilled, bundled by member type)?
Yes — cutting to length, punching and kit-bundling per greenhouse bay is a standard service and saves the erector weeks; drawings are all we need.
How is greenhouse tube priced?
Per tonne, like structural tube, with premiums for dipping-after-fabrication, kit processing and ZAM. Thin walls make the tonne count sensitive: check actual weights.
Standards & references: EN 10219 / EN 10240 · ASTM A500 / A123 · GB/T 3091 / NY/T 6
Sourcing for a specific application? CREATEEL exports carbon steel welded and seamless pipe, coated and galvanized pipe, fittings, forgings and machined parts — application-matched and fully certified. Send us your requirement.
