| Hot-Dip Galvanized Carbon Steel Pipe | Structural carbon steel with a zinc coating applied after fabrication; coating mass commonly selected to meet ISO 1461 requirements. | Approximately 235–350 MPa, depending on steel grade and tube specification. | Continuous zinc layer with sacrificial corrosion protection. | Typically about 45–85 μm per surface for many structural tube thicknesses; exact minimums depend on steel thickness and the applicable standard. | Very good | High | Welding, bolting, clamps, threaded fittings, and swaged or formed connections. Zinc fumes require proper controls during welding. | Primary frames, arches, columns, trusses, bracing, and high-load structures. | High strength, widely available, durable zinc protection, and good performance in humid environments. | Heavier than aluminum; cut or drilled areas may require zinc-rich repair treatment; surface appearance can vary. |
| Pre-Galvanized Steel Tube | Cold-formed or welded steel tube manufactured from galvanized sheet, often specified by zinc coating mass such as Z275. | Approximately 220–350 MPa, depending on the steel grade. | Factory-applied zinc coating before tube forming or welding. | For a 275 g/m² total coating mass, the nominal zinc thickness is approximately 20 μm per side, subject to standard and tolerance. | Good | High | Fast to cut and assemble with clamps or self-drilling fasteners. Welded edges and cut ends need additional protection. | Secondary framing, purlins, side rails, crop-support members, and light-to-medium duty structures. | Lower cost than many post-fabrication coatings; consistent factory finish; easy to process. | Welds, cut ends, and damaged areas have less protection than the original surface; generally less robust than hot-dip galvanizing after fabrication. |
| Powder-Coated Carbon Steel Pipe | Carbon steel tube with a cured thermoset powder coating over a prepared steel surface, normally with a corrosion-resistant primer system. | Approximately 235–350 MPa, depending on the underlying steel grade. | Polyester or epoxy-polyester powder coating; exterior-grade polyester is generally preferred for sunlight exposure. | Commonly about 60–120 μm for the complete powder layer; the specification should define the actual range. | Good to very good | High | Easy to fabricate before coating. Post-coating drilling, cutting, and welding require touch-up protection. | Visible frames, benches, trellis systems, doors, partitions, and structures where color and appearance matter. | Attractive finish, broad color selection, smooth surface, and good resistance to many fertilizers when properly specified. | Coating damage can expose steel; UV, abrasion, and chemical resistance depend strongly on resin type and pretreatment quality. |
| Zinc-Rich Painted Steel Pipe | Carbon steel protected by a zinc-rich primer and compatible intermediate or topcoat. | Approximately 235–350 MPa, depending on the steel grade. | Inorganic or organic zinc-rich primer, usually combined with an epoxy and/or weather-resistant topcoat. | System totals commonly range from about 100–250 μm, depending on the exposure category and paint system. | Very good when maintained | High | Can be fabricated before painting; repairs are practical with compatible zinc-rich materials and topcoats. | Large structures, coastal sites, areas requiring field repair, and projects with specified paint-system performance. | Flexible repair options, customizable protection, and strong performance when surface preparation is controlled. | Requires careful cleaning, application, drying, inspection, and periodic maintenance; poor preparation greatly reduces service life. |
| Aluminum Alloy Tube | Common architectural or structural aluminum alloys such as 6063-T5/T6 or 6061-T6; exact mechanical properties vary by temper. | Approximately 110–240 MPa, depending on alloy and temper. | Natural oxide film, anodizing, or exterior-grade powder coating. | Anodizing is commonly about 10–25 μm; powder coating is commonly about 60–120 μm. | Very good | Low | Extrusion-friendly; joined with bolts, clamps, dedicated connectors, or compatible welding procedures. Thermal expansion should be considered. | Lightweight arches, glazing bars, vents, doors, movable roofs, and corrosion-sensitive installations. | Approximately one-third the density of steel, naturally corrosion resistant, clean appearance, and easy handling. | Lower stiffness than steel for the same size; higher material cost; galvanic corrosion can occur when contacting dissimilar metals in moisture. |
| Stainless Steel Tube | Common austenitic grades include 304 and 316; grade selection should reflect chloride, fertilizer, and cleaning-chemical exposure. | Typically about 205–290 MPa minimum yield strength for common annealed grades. | Mill finish, brushed finish, electropolished finish, or passivated surface. | No applied metallic coating is normally required; protective performance depends on alloy and surface condition. | Excellent | High | Welding, orbital welding, clamps, and mechanical fittings. Weld discoloration should be cleaned and passivated where required. | Coastal greenhouses, hydroponic areas, fertilizer-handling zones, irrigation assemblies, and hygiene-sensitive components. | Excellent corrosion resistance, long service potential, cleanability, and strong performance in wet environments. | High purchase cost; chloride exposure can cause localized corrosion in unsuitable grades or poorly maintained surfaces. |
| PVC or uPVC Pipe | Rigid thermoplastic pipe selected by pressure class, temperature rating, and UV-stabilization requirements. | Not normally specified by yield strength for greenhouse structural design; stiffness and pressure rating are the controlling properties. | UV stabilizers, pigmentation, or an exterior protective layer; protection varies by formulation. | Not applicable as a metallic coating; wall thickness is selected by pipe class and application. | Good for water service | Very low | Solvent cement, threaded adapters, compression fittings, or mechanical couplings. Thermal movement and brittleness at low temperatures require consideration. | Irrigation lines, drainage, nutrient delivery, misting, and non-load-bearing utility systems. | Lightweight, low cost, electrically nonconductive, and resistant to many common water-treatment chemicals. | Generally unsuitable for primary structural frames; UV exposure, heat, impact, and chemical compatibility must be checked. |
| FRP or Fiberglass-Reinforced Plastic Tube | Glass-fiber-reinforced polymer profile selected by resin type, fiber direction, load, and environmental exposure. | Highly product-specific; design values commonly range from approximately 100–300 MPa in the principal fiber direction. | UV-resistant resin, gel coat, or an external veil layer. | Not normally specified as a metallic coating; protective surface layers are product-specific. | Very good | Very low | Bolting, bonded fittings, clamps, and specialized connectors. Drilling requires edge protection and suitable tools. | Corrosive irrigation zones, specialty structures, shade systems, and nonconductive applications. | Low weight, high resistance to many chemicals, and electrical nonconductivity. | Lower impact tolerance than steel, joining is less standardized, UV performance varies, and recycling can be difficult. |