GI Hollow Pipe: The Complete Engineering Specification and Structural Guide
Hexi, Tianjin, China – September 10, 2026
GI hollow pipe (Galvanized Iron Hollow Pipe, encompassing circular, square, and rectangular galvanized steel hollow sections) is a structural carbon steel tubular product protected by a zinc barrier layer to resist environmental rust, chemical oxidation, and mechanical weathering across building frameworks, agricultural greenhouses, solar racking, and highway infrastructure. This comprehensive technical guide delivers an in-depth engineering analysis of GI hollow pipe, comparing pre-galvanized versus post-fabrication hot-dip galvanized manufacturing processes, detailing dimensional size and weight metrics across Circular Hollow Sections (CHS), Square Hollow Sections (SHS), and Rectangular Hollow Sections (RHS), reviewing governing standards under ASTM A500, EN 10219, and BS 1387, and outlining certified procurement protocols from Cortec Steel.
GI Hollow Pipe Manufacturing Processes: Pre-Galvanized vs Hot-Dip Galvanized
Evaluating structural GI hollow pipe requires distinguishing between the two primary industrial zinc coating techniques, which establish differing protective lifespans and mechanical characteristics.
Pre-Galvanized GI Hollow Pipe (Continuous Coil Process)
Pre-galvanized hollow pipes (often called mill-galvanized or in-line galvanized) are cold-formed directly from continuous hot-dip galvanized steel coil strip (skelp).
- Production Method: Steel coils with mill-applied zinc layers pass through progressive roll-forming stands into circular, square, or rectangular profiles. The longitudinal seam is welded via high-frequency electric resistance welding (ERW).
- Weld Seam Metallizing: Because high-frequency welding burns away the original zinc layer along the longitudinal joint, modern production lines deploy automated thermal arc zinc spray systems to metalize and seal the exterior weld seam inline.
- Coating Mass: Typical zinc coating weights range from 60 to 180 g/m² (approx. 8 to 25 µm per side).
- Primary Scope: Indoor structural framing, light agricultural greenhouses, furniture tubing, electrical conduit, and moderate-humidity environments.
Post-Fabrication Hot-Dip Galvanized GI Hollow Pipe (Batch HDG)
Post-fabrication hot-dip galvanized hollow pipe is formed, welded, and sized as bare carbon steel tubular sections before undergoing full-immersion thermal galvanizing.
- Production Method: Welded hollow pipes are chemically pickled in acid baths to strip mill scale, treated with flux, and submerged entirely into a molten zinc kettle maintained at 445°C to 455°C (830°F to 850°F).
- Microstructural Bond: Iron atoms from the steel substrate diffuse into the molten zinc, forming three distinct intermetallic iron-zinc alloy layers (Gamma, Delta, and Zeta) beneath an outer layer of pure zinc (Eta).
- Coating Mass: Delivers heavy zinc protection typically exceeding 400 to 600 g/m² (55 to 85 µm nominal thickness), coating both the exterior and interior hollow surfaces completely.
- Primary Scope: Heavy civil engineering columns, marine piling structures, coastal solar racking, and severe industrial atmospheres.
GI Hollow Pipe Dimensional Specifications and Weight Chart
GI hollow pipe products are supplied in three primary geometric cross-sections: Circular (CHS), Square (SHS), and Rectangular (RHS). The table below details nominal dimensional parameters and calculated weights across popular structural sizes:
|
Section Geometry |
Metric Profile Dimensions (mm) |
Imperial Nominal Size (Inches) |
Wall Thickness (mm) |
Theoretical Weight (kg/m) |
Standard Governing Spec |
|---|---|---|---|---|---|
|
Round (CHS) |
OD 33.7 mm |
1 in. Nominal (NPS 1) |
2.60 mm |
1.99 kg/m |
BS 1387 / EN 10255 Class B |
|
Round (CHS) |
OD 48.3 mm |
1-1/2 in. Nominal (NPS 1-1/2) |
3.20 mm |
3.56 kg/m |
BS 1139 / EN 39 Scaffolding |
|
Round (CHS) |
OD 60.3 mm |
2 in. Nominal (NPS 2) |
3.60 mm |
5.03 kg/m |
ASTM A53 Grade B |
|
Round (CHS) |
OD 114.3 mm |
4 in. Nominal (NPS 4) |
4.50 mm |
12.18 kg/m |
ASTM A500 Grade B / C |
|
Square (SHS) |
25 x 25 mm |
1 x 1 in. |
1.50 mm |
1.06 kg/m |
ASTM A500 / EN 10219 |
|
Square (SHS) |
50 x 50 mm |
2 x 2 in. |
2.50 mm |
3.64 kg/m |
ASTM A500 Grade B |
|
Square (SHS) |
100 x 100 mm |
4 x 4 in. |
4.00 mm |
11.70 kg/m |
ASTM A500 Grade C |
|
Square (SHS) |
150 x 150 mm |
6 x 6 in. |
6.00 mm |
26.40 kg/m |
EN 10219 S355J2H |
|
Rectangular (RHS) |
50 x 25 mm |
2 x 1 in. |
2.00 mm |
2.19 kg/m |
ASTM A500 / EN 10219 |
|
Rectangular (RHS) |
80 x 40 mm |
3.15 x 1.57 in. |
3.00 mm |
5.21 kg/m |
ASTM A500 Grade B |
|
Rectangular (RHS) |
120 x 60 mm |
4.72 x 2.36 in. |
4.50 mm |
11.80 kg/m |
ASTM A500 Grade C |
|
Rectangular (RHS) |
200 x 100 mm |
8 x 4 in. |
6.30 mm |
28.10 kg/m |
EN 10219 S355J2H |
Governing Structural Standards and Mechanical Property Thresholds
Selecting the correct GI hollow pipe requires verifying structural yield strength, tensile boundaries, and elongation requirements to prevent buckling under compressive building loads.
ASTM A500 (Cold-Formed Welded Carbon Steel Tubing)
ASTM A500 is the dominant structural standard in North America for round, square, and rectangular hollow sections:
- Grade B: Minimum yield strength of 290 MPa (42,000 PSI) for shaped profiles (SHS/RHS) and 240 MPa (35,000 PSI) for round tubing (CHS), with 23% minimum elongation.
- Grade C: Minimum yield strength of 315 MPa (46,000 PSI) for shaped profiles and 317 MPa (46,000 PSI) for round tubing, delivering superior load-bearing capacity in multi-story columns.
EN 10219 (Cold-Formed Welded Structural Hollow Sections)
Widely specified across Europe and international infrastructure projects:
- S235JRH: Minimum yield strength of 235 MPa, suitable for general fencing, solar frame bracing, and light structures.
- S355J2H: High-strength structural grade delivering a minimum yield strength of 355 MPa and verified Charpy impact toughness (27 Joules minimum at -20°C), engineered for heavy crane booms, airport roof trusses, and dynamic wind-load applications.
Key Engineering Applications of GI Hollow Pipe
Due to its closed cross-sectional geometry, high torsional rigidity, and weather-resistant zinc barrier, GI hollow pipe serves essential functions across diverse industries:
Solar Photovoltaic Racking and Ground Mounts
Utility-scale solar farms deploy square and rectangular pre-galvanized and hot-dip Galvanized Steel Pipe hollow sections as torque tubes, purlins, and ground posts. The zinc coating prevents corrosive degradation from damp soil and atmospheric moisture over 25+ year project design lives.
Commercial Agricultural Greenhouses
Greenhouse construction requires structural members that withstand warm, humid atmospheres rich in chemical fertilizers and pesticides. Pre-galvanized circular and rectangular hollow pipes provide the necessary bending strength to support glass and polycarbonate panels without recurring painting maintenance.
Architectural Space Trusses and Building Columns
In modern commercial warehouses and distribution hubs, square and rectangular Hollow Sections serve as interior load-bearing columns. When combined with core Carbon Steel Pipe or standard ERW Steel Pipe utilities, contractors maximize structural efficiency while simplifying architectural cladding integration.
GI Hollow Pipe Sourcing, Inspection, and Quality Assurance Guidelines
Procuring industrial GI hollow pipe stock requires rigorous quality verification to ensure that weld seams, dimensional tolerances, and zinc coatings meet engineering design rules. Ensuring full compliance with ASTM A500, EN 10219, or BS 1387 prevents corner radius micro-cracking during cold bending and guarantees uniform load distribution.
Every order supplied by Cortec Steel includes traceable EN 10204 3.1 Mill Test Certificates (MTCs). These certificates verify chemical heat analysis, mechanical tensile and yield strength, corner radius geometry, magnetic zinc coating thickness tests (ASTM B499), and inline eddy current weld seam inspection. For custom structural cut lengths, specialized square/rectangular dimensions, and global logistics, contact the technical engineering desk at Cortec Steel today.
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