Hot-dip galvanized steel pipe is the structural backbone of most commercial greenhouses. This guide compares G60 and G90 coating weights for greenhouse frames, with selection guidance on lifespan, cost and the corrosion environment inside a typical glass or poly greenhouse.
Greenhouse structures have to carry glazing loads, wind, snow and crop hanging weight for 15–25 years, all while sitting in one of the most corrosive environments a steel frame can face: high humidity, frequent irrigation, fertilizer salt mist, and pesticide sprays. Hot-dip galvanized steel pipe is the standard framing material because the zinc coating sacrifices itself slowly to protect the steel underneath. The most common specification choice is between G60 and G90 coating weight, and getting that call wrong is the difference between a frame that lasts the life of the greenhouse and one that needs refurbishment in 8–10 years.
What G60 and G90 Mean for Greenhouse Service
The G designation is the total zinc coating weight on both sides of the steel in ounces per square foot. G60 means 0.60 oz/ft² total (about 85 μm average thickness), and G90 means 0.90 oz/ft² total (about 130 μm average). In a typical greenhouse environment, the zinc corrodes at roughly 1–2 μm per year on exposed surfaces, so G60 gives about 40–60 years of theoretical life on a clean surface, while G90 gives 60–90 years. In practice, the corners, weld zones and contact points consume zinc faster, so G60 frames in heavy fertilizer or sulfur fumigation environments may show red rust in 10–15 years, while G90 typically lasts the full greenhouse life.
When G60 Is the Right Specification
G60 hot-dip galvanized steel pipe is the standard specification for many greenhouse structures in mild climates, for poly houses with shorter design life (8–15 years), and for low-corrosion crops such as leafy greens in well-ventilated houses. G60 also fits projects where the budget is tight and the structure is designed to be replaceable, like seasonal poly tunnels. In this case, the extra cost of G90 is not justified because the poly and the frame will both be replaced before the coating is consumed.
When G90 Is the Necessary Upgrade
G90 hot-dip galvanized steel pipe is required for glass or rigid polycarbonate greenhouses with a 20–30 year design life, for houses growing tomatoes, cucumbers, peppers and other high-value crops that require sulfur fumigation, and for any structure near the coast or in regions with high humidity and temperature swings. The thicker coating also gives better protection at welds, cut ends and bolt connections, which are the first areas to fail on a G60 frame in a corrosive environment. For Venlo-style glass greenhouses and large gutter-connected houses, G90 is the practical default.
Pipe Size, Strength and Connection Detail
For greenhouse framing, the typical pipe sizes are 21.3 mm (1/2"), 26.9 mm (3/4"), 33.4 mm (1"), 42.4 mm (1-1/4"), 48.3 mm (1-1/2") and 60.3 mm (2"), with wall thickness from 1.5 mm to 3.2 mm depending on the span and load. Most manufacturers use ASTM A53 Grade A or Grade B pipe as the substrate, hot-dip galvanized to ASTM A123. Connection design matters: avoid trapping water on horizontal members, and where cuts and welds are made in the field, touch up with a zinc-rich paint to restore the coating. Bolted connections should use galvanized or stainless hardware matched to the frame coating.
What to Specify on the Greenhouse Pipe RFQ
State the substrate standard (ASTM A53 Grade A or B), the coating standard (ASTM A123), the coating weight (G60 or G90), the nominal pipe size and wall thickness, and the length (typically 6 m random or cut-to-length). Specify that cut ends and weld zones be repaired with zinc-rich primer in the shop, and that the coating be free of bare spots, dross inclusions and flux residue. For export orders, confirm the pipe is bundled with non-staining spacers and shipped in containers with desiccant to prevent wet-storage stain on the zinc surface.
Related Resources from Baobin Steel
- Carbon steel pipe catalog – A53 and A106 base pipe for galvanizing
- Mild steel overview – grades and standards
- Request a quote – send your frame drawing for galvanized greenhouse pipe pricing