Products Description
A500 GRA/GRB hot-dip galvanized tubing combines the structural integrity of ASTM A500 cold-formed carbon steel hollow sections with the long-term corrosion protection of a metallurgically bonded zinc coating. The base tube is produced by the electric resistance welding (ERW) process, formed from steel coil, welded along the longitudinal seam, and then fully immersed in molten zinc at approximately 450 °C to create a zinc–iron alloy coating that is bonded to the steel-not merely applied over it. The result is a load-bearing structural tube suitable for outdoor, humid, and moderately corrosive environments where black steel would require frequent maintenance or coating repair.
The "GRA / GRB" designation refers to ASTM A500 Grade A and Grade B. Both grades are covered under the same ASTM A500/A500M specification for cold-formed welded and seamless carbon steel structural tubing in round, square, rectangular, and special shapes. Grade B is the most widely specified grade for hollow structural sections (HSS) in export markets, while Grade A serves lighter structural and non-critical load-bearing applications.
1.Common Export Sizes
Export orders typically fall within the ranges below. Custom sizes, intermediate wall thicknesses, and non-standard lengths are available subject to mill confirmation.
》Round Tubing (CHS - Circular Hollow Section)
| Nominal Size | Outer Diameter (mm) |
Typical Wall Thickness (mm) |
Standard Length (m) |
| 1/2″ | 21.3 | 1.5 – 3.0 | 5.8 / 6.0 / 12.0 |
| 3/4″ | 26.7 | 1.5 – 3.0 | 5.8 / 6.0 / 12.0 |
| 1″ | 33.4 | 1.5 – 4.0 | 5.8 / 6.0 / 12.0 |
| 1-1/4″ | 42.3 | 1.5 – 4.0 | 5.8 / 6.0 / 12.0 |
| 1-1/2″ | 48.3 | 1.5 – 4.0 | 5.8 / 6.0 / 12.0 |
| 2″ | 60.3 | 1.5 – 4.0 | 5.8 / 6.0 / 12.0 |
| 2-1/2″ | 76.1 | 1.5 – 6.0 | 5.8 / 6.0 / 12.0 |
| 3″ | 88.9 | 2.0 – 6.0 | 5.8 / 6.0 / 12.0 |
| 4″ | 114.3 | 2.0 – 8.0 | 5.8 / 6.0 / 12.0 |
| 5″ | 141.3 | 3.0 – 8.0 | 5.8 / 6.0 / 12.0 |
| 6″ | 168.3 | 3.0 – 10.0 | 5.8 / 6.0 / 12.0 |
| 8″ | 219.1 | 3.2 – 12.0 | 5.8 / 6.0 / 12.0 |
| 10″ | 273 | 4.0 – 12.0 | 5.8 / 6.0 / 12.0 |
| 12″ | 323.8 | 5.0 – 14.0 | 5.8 / 6.0 / 12.0 |
| 14″ | 355.6 | 6.0 – 16.0 | 5.8 / 6.0 / 12.0 |
| 16″ | 406.4 | 6.0 – 16.0 | 5.8 / 6.0 / 12.0 |
Broader export OD range: 21.3 mm to 610 mm. Larger diameters may be available with mill confirmation.
》Square Tubing (SHS - Square Hollow Section)
| Outer Dimension (mm) | Typical Wall Thickness (mm) | Standard Length (m) |
| 20 × 20 | 1.5 – 3.0 | 5.8 / 6.0 / 12.0 |
| 25 × 25 | 1.5 – 3.0 | 5.8 / 6.0 / 12.0 |
| 30 × 30 | 1.5 – 4.0 | 5.8 / 6.0 / 12.0 |
| 40 × 40 | 1.5 – 5.0 | 5.8 / 6.0 / 12.0 |
| 50 × 50 | 2.0 – 6.0 | 5.8 / 6.0 / 12.0 |
| 60 × 60 | 2.0 – 6.0 | 5.8 / 6.0 / 12.0 |
| 75 × 75 | 2.5 – 8.0 | 5.8 / 6.0 / 12.0 |
| 80 × 80 | 2.5 – 8.0 | 5.8 / 6.0 / 12.0 |
| 100 × 100 | 3.0 – 10.0 | 5.8 / 6.0 / 12.0 |
| 120 × 120 | 3.0 – 10.0 | 5.8 / 6.0 / 12.0 |
| 150 × 150 | 4.0 – 12.0 | 5.8 / 6.0 / 12.0 |
| 200 × 200 | 5.0 – 14.0 | 5.8 / 6.0 / 12.0 |
| 250 × 250 | 6.0 – 16.0 | 5.8 / 6.0 / 12.0 |
| 300 × 300 | 6.0 – 16.0 | 5.8 / 6.0 / 12.0 |
| 400 × 400 | 8.0 – 16.0 | 5.8 / 6.0 / 12.0 |
Packaging for Export
- Small and medium outside dimensions (typically ≤ 300 mm OD / square): bundled with steel strips, typically 5–8 strips per bundle depending on bundle weight and size; plastic end caps optional; waterproof paper or plastic wrapping available for sea shipment.
- Large outside dimensions (typically > 300 mm OD / square): loose packing or piece-by-piece handling, with lifting points and edge protection as required.
- Bundle identification: each bundle tagged with heat number, size, grade, and coating specification for traceability.
- Container or breakbulk: bundled tube is suitable for container loading up to 12 m lengths; longer or heavier bundles can be shipped breakbulk or in open-top containers subject to forwarder confirmation.
Technical Specifications
1. Chemical Composition (ASTM A500, ladle analysis)
| Element | Grade A (GRA) | Grade B (GRB) |
| Carbon (C), max % | 0.26 | 0.26 |
| Manganese (Mn), max % | 1.35 | 1.35 |
| Phosphorus (P), max % | 0.035 | 0.035 |
| Sulfur (S), max % | 0.035 | 0.035 |
| Copper (Cu), min % when copper-bearing specified | 0.2 | 0.2 |
Data reflect the 2026 consolidated reference for ASTM A500 Grades A–D. Some mill product analyses may show slightly different manganese limits depending on heat and product analysis provisions; the mill test certificate governs each shipment.
2. Mechanical Properties (minimum values)
| Section Shape | Grade | Yield Strength, min | Tensile Strength, min | Elongation in 50 mm, min |
| Round (CHS) | GRA | 228 MPa (33 ksi) | 310 MPa (45 ksi) | 0.25 |
| Round (CHS) | GRB | 317 MPa (46 ksi) | 400 MPa (58 ksi) | 0.23 |
| Square / Rectangular / Shaped | GRA | 269 MPa (39 ksi) | 310 MPa (45 ksi) | 0.25 |
| Square / Rectangular / Shaped | GRB | 317 MPa (46 ksi) | 400 MPa (58 ksi) | 0.23 |
3. Hot-Dip Galvanized Coating
The zinc coating is applied after tube fabrication by full immersion in molten zinc, producing a metallurgically bonded zinc–iron alloy layer. Coating requirements are typically specified to ASTM A123/A123M (North American and international projects) or EN ISO 1461 (European and many export markets).
ASTM A123 minimum average coating thickness for Pipe & Tubing:
| Steel Thickness Range | Minimum Average Coating Thickness Grade |
| < 1.6 mm | 45 |
| ≥ 1.6 mm to < 3.2 mm | 45 |
| ≥ 3.2 mm to < 4.8 mm | 75 |
| ≥ 4.8 mm to < 6.4 mm | 75 |
| ≥ 6.4 mm to < 16.0 mm | 75 |
| ≥ 16.0 mm | 75 |
Source: ASTM A123 Table 1, Pipe & Tubing category. The "grade" number corresponds to the minimum average coating thickness in micrometres (μm) for the lot average. Individual specimens are permitted to fall one coating grade below the required value.
Typical export zinc coating ranges:
| pecification | Typical Coating Thickness | Typical Coating Weight |
| ASTM A123 minimum (commercial) | 45–75 μm | approx. 320–550 g/m² |
| Enhanced export specification | 70–120 μm | 500–850 g/m² |
| High-corrosion specification | 85–150 μm | 600–1,000+ g/m² |
Coating weight is commonly expressed as total zinc on both surfaces (g/m²). A coating of 45 μm corresponds approximately to 320 g/m²; 75 μm corresponds approximately to 530 g/m². Z275 (275 g/m² total) and Z450/Z600 are common commercial callouts, although for hot-dip galvanized structural tubing the μm-based ASTM A123 grade is the more appropriate controlling specification.
4. Dimensional Tolerances (ASTM A500)
Round tubing - outside diameter tolerance:
| OD Range | Tolerance |
| ≤ 48.3 mm | ± 0.40 mm |
| > 48.3 to ≤ 101.6 mm | ± 0.79 mm |
| > 101.6 to ≤ 203.2 mm | ± 1.59 mm |
| > 203.2 mm | ± 0.75% of OD |
Square / rectangular tubing - outside dimension tolerance:
| Largest Outside Dimension Across Flats | Tolerance |
| ≤ 63.5 mm (2½″) | ± 0.50 mm |
| > 63.5 to ≤ 88.9 mm | ± 0.64 mm |
| > 88.9 to ≤ 139.7 mm | ± 0.76 mm |
| > 139.7 mm | ± 1% |
Wall thickness tolerance: −10% of specified nominal wall, no positive limit; the average wall must be consistent with the ordered mass per unit length, which is the controlling dimension for structural design. The weld area is excluded from the wall thickness tolerance requirement.-14-45
Other geometric tolerances:
- Squareness of sides: ±2° maximum deviation from 90°.
- External corner profile: maximum 3t (three times specified wall thickness).
- Straightness / twist: specified in ASTM A500; twist limits vary by longest side dimension and are typically on the order of 1.4–3.1 mm per metre for common export sizes.
- Length tolerance: +50.8 mm / −0 mm on ordered lengths unless otherwise agreed.
Applications
A500 GRA/GRB hot-dip galvanized tubing is specified where structural load-bearing capacity and outdoor corrosion resistance are both required. Because A500 is a structural specification-not a pressure-pipe specification-it is intended for welded, riveted, or bolted construction rather than fluid transmission under pressure.
| Sector | Typical Uses |
| Building & architecture | Building frames, columns, beams, roof purlins, mezzanine structures, stadium and exhibition structures, factory workshop steelwork |
| Infrastructure | Bridge components and auxiliary supports, highway guardrails, tunnel structural members, sign gantries, transmission towers |
| Solar & renewable energy | Solar panel mounting frames, tracker structures, support piles |
| Agriculture | Agricultural greenhouses, livestock equipment frames, irrigation structure supports |
| Fencing & barriers | Security fencing posts and rails, temporary safety barriers, crowd-control barricades |
| Scaffolding & access | Scaffolding frames, walkway supports, working platforms (subject to project-specific scaffolding standards) |
| General fabrication | Machine frames, equipment skids, storage racking (light-to-medium duty for GRA; heavier duty for GRB), handrails, stair stringers, mezzanine deck supports |
Grade selection guide:
GRA is suited to light structural members, fencing, railings, sign posts, bracing, and general fabrication where the design loads are moderate.
GRB is the default choice for building frames, bridge components, heavy machinery bases, load-bearing columns, and transmission towers-applications that represent the majority of structural hollow section demand.
FAQ
Q1: What is the practical difference between A500 GRA and GRB?
GRA is the entry-level grade under ASTM A500, with a minimum yield of 228 MPa (33 ksi) for round tubing and 269 MPa (39 ksi) for square/rectangular tubing. GRB has a minimum yield of 317 MPa (46 ksi) for both round and shaped sections, along with a higher minimum tensile strength of 400 MPa (58 ksi) versus 310 MPa (45 ksi) for GRA. In export practice, GRB is the default specification for load-bearing structural hollow sections; GRA is selected when design loads are light and material cost optimization is the priority.
Q2: Is the galvanized coating suitable for outdoor exposure without painting?
Yes, for most atmospheric exposure conditions. Hot-dip galvanizing to ASTM A123 provides a metallurgically bonded zinc coating that protects the steel both as a barrier and by sacrificial action at scratches and cut edges. In moderate outdoor environments, a properly applied HDG coating can provide 25 years or more of maintenance-free service, with longer life in benign atmospheres and shorter intervals in aggressive industrial or coastal environments. For severely corrosive environments (C4–C5 per ISO 12944), a duplex system-HDG plus a suitable paint topcoat-should be considered.
Q3: What is the difference between hot-dip galvanized and pre-galvanized tubing?
Hot-dip galvanized (HDG) tubing is fabricated first and then fully immersed in molten zinc. The coating forms a zinc–iron alloy layer that is metallurgically bonded to the steel, including at cut ends and weld seams, and is generally thicker and more durable. Pre-galvanized tubing is made from zinc-coated steel coil; the coating is present before welding and forming, so weld seams and cut ends may have exposed or thinner zinc unless post-treatment is applied. For structural export projects requiring long service life and coating integrity at connections, HDG to ASTM A123 is the appropriate specification.
Q4: Can galvanized A500 tubing be welded on site?
Yes, but precautions are required. Welding through zinc generates zinc oxide fume, so adequate ventilation and respiratory protection are essential. The zinc coating should be removed 25–50 mm back from the weld zone before welding, and the weld area should be recoated with a zinc-rich cold galvanizing compound after welding to restore corrosion protection. Welding procedures should account for the slightly lower effective wall thickness at the weld preparation and the heat input effects on the cold-formed section.
Q5: Is A500 tubing a pressure pipe?
No. ASTM A500 is a structural tubing specification, not a pressure-pipe specification. It does not require hydrostatic testing for pressure retention, and it is intended for welded, riveted, or bolted structural applications under load. For pressure service (water, steam, gas, air), ASTM A53 or another pressure-pipe specification should be used. If A500 tubing is used in a system that also conveys fluid, the design engineer must confirm that the structural grade and coating are appropriate for the combined service conditions.
Q6: What zinc coating weight or thickness should I specify for export?
For general structural export, specify ASTM A123 coating grade 45 or 75 depending on steel thickness, or EN ISO 1461 with a minimum average thickness of 45–85 μm depending on wall thickness. A common enhanced export specification is 70–120 μm (approximately 500–850 g/m²) for projects requiring longer corrosion protection or exposure to humid coastal atmospheres. Specify the requirement in μm or as an ASTM A123 grade rather than only as g/m², because g/m² is a mass-per-area expression and does not directly translate to a single coating thickness without knowing the zinc density and coating structure.
Q7: Can you supply custom lengths and cut-to-length programs?
Yes. Standard export lengths are 5.8 m, 6.0 m, 11.8 m, and 12.0 m. Custom lengths, multiple lengths per bundle, and cut-to-length programs with fixed or random patterns can be arranged, subject to minimum order quantities and mill scheduling. Length tolerance is typically +50.8 mm / −0 mm on ordered lengths unless a tighter tolerance is agreed.
Q8: What is the minimum order quantity (MOQ)?
MOQ is typically 2 tons per size and specification, with mixed sizes acceptable within a single order. For trial orders or project-specific requirements, lower quantities may be possible by arrangement. Lead time is commonly 7–15 working days after deposit for standard sizes, with longer lead times for large-diameter, heavy-wall, or custom-coated items
Our address
Rm1406,14th/F No 208, Hongqi Road, Nankai Dist, Tianjin City ,China
Phone Number (whatsApp/Wechat)
+8616622033809
alisa@tjshenzhoutong.com
Hot Tags: a500 gra / grb hot-dip galvanized round & square tubing, China a500 gra / grb hot-dip galvanized round & square tubing manufacturers, suppliers, factory, galvanized available pipe, galvanized coated pipe, galvanized ready to ship pipe, galvanized red pipe, galvanized threaded pipe, galvanized yellow pipe
