Hot-Dip Galvanized Round Steel Pipe is a circular welded steel tube processed with a hot-dip galvanized coating after pipe forming and welding. The round section is easy to fabricate, clamp, weld and install, while the galvanized surface provides additional protection where the pipe is exposed to rain, humidity and outdoor conditions.
The product covers two different purchasing needs. For guardrails, handrails, greenhouse structures and steel supports, buyers mainly look at outside diameter, wall thickness, steel grade and dimensional accuracy. For water or other fluid-service applications, the pipe must additionally meet the required pressure-service standard and inspection requirements.
Q235B is suitable for many conventional structural and fabrication applications. Q355B can be selected where the design calls for higher material strength. Fixed-length cutting and other processing can be arranged before delivery.
|
DN |
Outside Diameter (mm) |
Common Name |
Common Wall Thickness (mm) |
Typical Use |
|
DN15 |
21.3 |
4-in round pipe |
1.5 / 1.8 / 2.0 / 2.5 |
Small guardrails, conduit, handrails |
|
DN20 |
26.8 |
6-in round pipe |
1.5 / 1.8 / 2.0 / 2.5 |
Guardrail rails, light supports |
|
DN25 |
33.7 |
1-in round pipe |
1.8 / 2.0 / 2.5 / 2.75 / 3.0 |
Guardrail posts, greenhouse members |
|
DN32 |
42.4 |
1.2-in round pipe |
2.0 / 2.5 / 2.75 / 3.0 / 3.25 |
Greenhouse arch tubes |
|
DN40 |
48.3 |
1.5-in round pipe |
2.0 / 2.5 / 2.75 / 3.0 / 3.5 |
Greenhouse arches, railings, support tubes |
|
DN50 |
60.3 |
2-in round pipe |
2.5 / 2.75 / 3.0 / 3.25 / 3.5 |
Main greenhouse arches, medium posts |
|
DN65 |
76.1 |
2.5-in round pipe |
2.75 / 3.0 / 3.25 / 3.5 / 4.0 |
Monitoring poles, structural columns |
|
DN80 |
88.9 |
3-in round pipe |
3.0 / 3.5 / 4.0 / 4.5 |
Lighting poles, heavy greenhouse posts |
|
DN100 |
114.3 |
4-in round pipe |
3.0 / 3.5 / 4.0 / 4.5 / 5.0 |
Large posts, water pipe, main supports |
|
DN125 |
139.7 |
5-in round pipe |
3.5 / 4.0 / 4.5 / 5.0 |
Fluid lines, heavy supports |
|
DN150 |
168.3 |
6-in round pipe |
4.0 / 4.5 / 5.0 / 6.0 |
Main water lines, large structural columns |
|
DN200 |
219.1 |
8-in round pipe |
4.5 / 5.0 / 6.0 / 8.0 |
Municipal pipes, heavy structural work |
For international orders, always confirm DN, outside diameter and wall thickness together. DN is a nominal designation and does not by itself define the actual outside diameter.
|
Item |
Specification |
|
Product |
Hot-Dip Galvanized Round Steel Pipe |
|
Steel grade |
Q235B, Q355B |
|
Manufacturing |
Cold forming + high-frequency welding |
|
Common diameter range |
DN15–DN200 |
|
Outside diameter |
21.3–219.1 mm in the listed sizes |
|
Wall thickness |
1.5–8.0 mm, depending on diameter |
|
Standard length |
6 m |
|
Custom length |
3–12 m |
|
Surface |
Hot-dip galvanized |
|
Galvanizing temperature |
Approx. 450°C |
|
Typical processing |
Cutting, drilling, bending, welding |
|
Main uses |
Guardrails, handrails, greenhouse structures, supports, columns, selected fluid |
The pipe is produced as a welded round tube, then galvanized after the required pipe section has been formed.
Steel strip → forming → high-frequency welding → sizing and straightening → cutting → degreasing → pickling → rinsing → fluxing → drying → hot-dip galvanizing → cooling → passivation / finishing → inspection → packing
The high-frequency welding stage creates the longitudinal seam. It should therefore be described as a high-frequency welded round steel pipe, not a seamless pipe.
Before galvanizing, the steel surface needs to be clean enough for the zinc to bond properly. After galvanizing, the pipe is inspected again for coating, straightness, dimensions and visible defects.
The zinc layer separates the steel from atmospheric moisture and oxygen. Zinc also provides sacrificial protection around small areas of coating damage.
For an outdoor handrail, greenhouse frame or support structure, this means the main corrosion-protection work is completed before installation.
The galvanized coating does not mean the pipe can be permanently exposed to every corrosive medium without further consideration. Coastal salt spray, aggressive chemicals, standing water and continuous immersion require a more specific corrosion assessment.
Wall thickness should follow the job rather than the pipe name.
|
Wall Thickness |
Typical Direction |
|
1.5–2.0 mm |
Light guardrails, small frames, lighter greenhouse members |
|
2.5–3.0 mm |
Medium posts, supports and agricultural structures |
|
3.0–4.0 mm |
Heavier supports, columns and larger structural members |
|
4.0–8.0 mm |
Heavy structural or specific fluid-service requirements |
The final thickness depends on span, load, support spacing, wind conditions, connection method or fluid pressure.
Q235B is commonly used for general guardrails, greenhouse structures, support frames, municipal fabrication and other conventional steelwork.
Q355B is used when the structural design requires a higher-strength steel grade, especially for heavier loads or more demanding support conditions.
Changing the steel grade does not automatically allow the wall thickness or pipe diameter to be reduced. The complete member still needs to satisfy the design calculation.
The end use should be stated before quotation.
For guardrails, greenhouse frames, handrails, equipment supports and steel structures, dimensional accuracy and structural requirements are the main concerns.
For water and other fluid delivery, the applicable pipe standard, pressure rating, wall thickness, weld quality and inspection requirements also need to be specified.
For example, China's current GB/T 3091 standard applies to welded steel pipes for low-pressure fluid delivery. It should not be used as a generic standard for every galvanized structural round tube.
This distinction helps prevent a common procurement mistake: buying a pipe by diameter alone without checking what the pipe is actually designed to do.
The circular section is convenient for gripping and easy to connect to posts, brackets and frames.
Common sizes are used for arch tubes, posts, rails and other agricultural structures exposed to humidity and repeated wet-dry cycles.
Applications include roadside barriers, fences, parking shelters, light support frames and similar outdoor structures.
Can be used for selected supports, auxiliary frames and outdoor equipment structures when a round section is appropriate.
Larger diameters can be selected for poles and columns according to the structural requirement.
Suitable only when the pipe grade, dimensions and applicable service standard meet the project requirement.
For self-built houses and residential courtyards, black steel pipe often requires repeated rust removal and repainting after prolonged outdoor exposure.
Hot-dip galvanized round pipe can be installed without a separate large-scale anti-corrosion painting process. According to the supplied project record, outdoor courtyard railings remained free from visible widespread rust and coating failure after more than three years.
During renovation of older residential communities, galvanized round pipe was used for corridor handrails, roadside guardrails and parking-shelter supports.
The finished galvanized surface allowed the contractor to proceed directly with installation, reducing site coating work and keeping the finished appearance consistent.
The choice depends on the structure and appearance.
Round pipe is useful when the structure needs a circular profile, easy hand contact, smooth visual lines or convenient connection with clamps and circular fittings.
Square and rectangular tubes provide flat faces and are often easier to align when the project consists mainly of straight frames and plate connections.
For handrails and tubular guardrails, round pipe is usually the more natural choice. For rectangular frames, square or rectangular hollow sections may be more efficient.
Black round pipe has no factory zinc protection and normally needs another corrosion-protection system for outdoor service.
Galvanized round pipe arrives with the zinc coating already applied. This removes a major field coating step and reduces the need for routine repainting under normal exposure.
The difference is most useful on projects where many individual pipes are installed outdoors and later maintenance is difficult, such as guardrails, greenhouse frames, rooftop structures and municipal facilities.
For project orders, major fabrication can be completed before delivery.
Available processing includes:
Fixed-length cutting
Drilling and punching
Bending
End preparation
Welding and fabricated assemblies
Where possible, final cutting and drilling should be completed before galvanizing so that the processed member receives the corrosion-protection treatment as a finished component.
If cutting or drilling is performed after galvanizing, exposed steel should be cleaned and repaired with a suitable zinc-rich coating.
Quality inspection covers both the pipe and the galvanized coating.
Base material: Q235B or Q355B, with agreed material documentation.
Dimensions: outside diameter and wall thickness.
Geometry: roundness and straightness.
Weld: high-frequency welded seam condition.
Length: fixed-length accuracy.
Coating: coverage, thickness and obvious surface defects.
Packing: bundle stability and protection during transportation.
For fluid-service orders, additional testing should follow the specified pipe standard and project requirements.
Normal outdoor exposure can be handled with a suitable galvanized specification, but coastal and industrial environments should not all be treated the same.
Near the coast, salt-laden air can accelerate zinc consumption. In high-humidity buildings, condensation can become the main corrosion factor. Chemical plants may introduce gases or liquids that behave differently from ordinary atmospheric exposure.
The correct approach is to match the zinc requirement and pipe specification to the actual environment.
Continuous seawater immersion is also different from ordinary outdoor exposure and should be treated as a separate corrosion-design condition.
Our supply chain in Tianjin Daqiuzhuang gives buyers access to steel processing, pipe production, galvanizing and downstream fabrication resources within the same steel-producing region.
Multiple sizes: DN15–DN200 covers common applications from small handrails to larger structural and fluid-service pipe.
Material selection: Q235B and Q355B can be supplied according to the structural requirement.
Fixed-length supply: 3–12 m cutting is available, with 6 m as a common standard length.
Project processing: Cutting, drilling, bending and other agreed fabrication can be completed before delivery.
Application-based quotation: structural pipe and fluid-service pipe are handled according to their different technical requirements.
Inspection documents: material certificates and galvanizing inspection records can be supplied for project orders.
Export packing: bundles can be prepared with moisture-resistant protection for overseas transportation.
The benefit for the buyer is fewer separate suppliers to coordinate for steel tube, galvanizing, processing and export preparation.
For quotation, provide:
Application: structure, greenhouse, guardrail, fluid service, etc.
DN or outside diameter
Wall thickness
Steel grade
Length
Galvanizing requirement
Processing requirement
Quantity
A clear request such as:
Q235B / DN50 / OD 60.3 mm / 3.0 mm wall / hot-dip galvanized / 6 m / 100 tons
allows the supplier to quote the correct product without guessing what “2-inch galvanized pipe” is intended to mean.
No. The product described here is a high-frequency welded round steel pipe. It should not be advertised as seamless.
The listed DN50 pipe has an outside diameter of 60.3 mm. Confirm the actual outside diameter before ordering fittings or clamps.
Yes, where the pipe meets the required low-pressure fluid-service standard and project specification. The applicable standard should be confirmed before ordering.
Yes. The supplied range is 3–12 m, with 6 m being a common standard length.
Yes. Q355B can be specified for projects requiring a higher-strength steel grade. The final pipe diameter and wall thickness should still follow the structural design.
Yes. Welding damages the zinc coating around the heated area. The affected zone should be cleaned and repaired with a suitable zinc-rich coating after welding.
Yes, but significant bending can damage the galvanized layer. Where the final shape is known, it is preferable to complete the main forming work before galvanizing.
The supplied sizes include approximately 1.5–3.5 mm for many common greenhouse applications. The actual choice should consider span, wind load, member position and greenhouse design.
Yes. Hot-dip galvanized round pipe is designed for corrosion protection under outdoor atmospheric exposure, so a separate primary anti-corrosion painting process is generally not required for normal conditions.
Yes, but the zinc specification should be matched to the salt exposure. Strong coastal conditions may require a higher coating requirement and additional corrosion considerations.
Zinc protects the steel but is gradually consumed by the environment. Service life depends on coating thickness, humidity, salt exposure, chemicals, water retention and handling. No single service-life figure applies to every installation.
Material certificates, galvanizing inspection records and other agreed quality documents can be supplied. Third-party inspection can also be arranged for project orders.
Address
Secondary Arterial Road No. 2-1, Expansion Area of Daqiuzhuang Industrial Zone, Jinghai District, Tianjin, China
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