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What are Galvanized Steel Pipes? Their Specification, Welding, and Applications

Galvanized Steel Pipe

Introduction Of Galvanized Steel Pipe

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Galvanized steel pipe is a steel pipe made by coating a layer of zinc on the surface of ordinary steel pipe (carbon steel pipe). Zinc has active chemical properties and can form a dense oxide film, thereby isolating oxygen and moisture and preventing the steel pipe from rusting.GI steel pipe is a metal pipe with zinc coating on the surface of ordinary steel pipe to prevent corrosion. It is divided into hot-dip galvanizing and electro-galvanizing. Hot-dip galvanized steel pipes are immersed in molten zinc liquid (about 450°C) to form a thicker zinc layer (50-150μm), which has strong corrosion resistance and is suitable for outdoor or humid environments; electro-galvanized steel pipe adopts electrolysis process, the zinc layer is thinner (5-30μm), the cost is lower, and it is mostly used indoors.

Specifications Of Galvanized Steel Pipe

Size And Diameter

1.Nominal diameter (DN): The common range is DN15 ~ DN600 (i.e. 1/2 inch ~ 24 inches).

2.Outer diameter (OD):

(1).Small diameter pipe: such as DN15 (21.3mm), DN20 (26.9mm).

(2).Medium and large diameter pipe: such as DN100 (114.3mm), DN200 (219.1mm).

3.British specifications: Some are still expressed in inches, such as 1/2", 3/4", 1", etc.

Wall Thickness And Pressure Rating

1.Ordinary wall thickness (SCH40): suitable for low-pressure fluid transportation (such as water pipes, gas pipes).

2.Thickened wall thickness (SCH80): higher pressure resistance, used for structural support or high-pressure scenarios.

3.National standard wall thickness: As specified in GB/T 3091, the wall thickness of DN20 galvanized steel pipe is 2.8mm (ordinary grade).

Length

1.Standard length: usually 6 meters/piece, 3m, 9m or 12m can also be customized.

2.Fixed length: cut according to project requirements, ±10mm error is allowed.

Materials And Standards

1.Base pipe material: Q235 carbon steel, Q345 low alloy steel, etc.

2.Galvanized layer thickness:

(1).Hot-dip galvanizing: ≥65μm (GB/T 3091).

(2).Electrogalvanizing: 5~30μm (weak rust resistance).

3.Implementation standards:

(1).China: GB/T 3091 (welded galvanized pipe), GB/T 13793 (seamless galvanized pipe).

(2).International: ASTM A53 (American standard), EN 10240 (European standard).

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Galvanized Steel Pipe Welding Process

Size And Diameter

Welding method: Commonly used welding methods include manual arc welding, gas shielded welding, CO2 gas shielded welding, etc. Choosing a suitable welding method can improve welding quality.

Welding preparation: Before welding, the surface contaminants such as paint, rust and dirt in the welding area need to be removed to ensure the quality of the weld.

Welding process: During welding, the current, voltage and welding speed should be controlled to avoid problems such as undercut and incomplete penetration. After welding, cooling and trimming should be carried out to prevent deformation and cracks.

Quality control: During welding, attention should be paid to the flatness and smoothness of the weld to avoid defects such as pores and slag inclusions. If welding quality problems are found, they should be handled and repaired in a timely manner.

Application Of Galvanized Steel Pipe

Building And Structural Engineering

1.Building scaffolding

Use: temporary support for construction, external wall work platform.

Specifications: DN40~DN150, wall thickness ≥3.0mm (SCH40).

Advantages: high strength, easy disassembly and assembly, more resistant to rust than ordinary steel pipes.

2.Steel structure auxiliary parts
Use: stair handrails, roof trusses, fence columns.

Features: Surface galvanizing can be used outdoors for a long time, reducing maintenance costs.

3. Building drainage system
Use: rainwater pipes, balcony drainage pipes.

Specifications: DN50~DN200, hot-dip galvanizing.

Municipal And Public Engineering

1.Water supply pipelines
Use: community water supply, fire water pipelines (low pressure).

Requirements: hot-dip galvanizing, in accordance with GB/T 3091 standard.

2.Gas transmission
Use: low-pressure natural gas, liquefied petroleum gas (LPG) pipelines.

Note: Welds must be strictly inspected to prevent leakage.

3.Power and communication protection pipes

Application: cable threading pipes, underground communication pipes.

Specifications: DN20~DN100, electrogalvanizing is sufficient (low cost).

Industrial Field

1.Mechanical equipment frame

Application: conveyor bracket, equipment guardrail.

Advantages: resistant to slight corrosion, suitable for workshop environment.

2.Ventilation system

Application: factory exhaust duct, air conditioning supply duct.

Features: galvanized layer can prevent moisture and rust, and extend service life.

3.Chemical industry and environmental protection

Application: low-pressure transmission pipelines for non-strong acid and strong alkali media (such as wastewater treatment).

Restrictions: not suitable for highly corrosive environments such as hydrochloric acid and sulfuric acid.

Agriculture And Transportation

1.Agricultural greenhouse support

Application: greenhouse frame, irrigation water pipe.

Specifications: DN15~DN50, thin-wall electrogalvanized pipe.

2. Traffic facilities
Applications: highway guardrails, street light poles, sign support poles.
Features: hot-dip galvanized, strong outdoor weather resistance.

Features: Surface galvanizing can be used outdoors for a long time, reducing maintenance costs.

3. Building drainage system
Use: rainwater pipes, balcony drainage pipes.

Specifications: DN50~DN200, hot-dip galvanizing.

ROYAL GROUP

Address

Kangsheng development industry zone,
Wuqing district, Tianjin city, China.

E-mail

sales01@royalsteelgroup.com
chinaroyalsteel@163.com(Factory Contact)

Phone

Sales Manager: +86 153 2001 6383‬

Hours

Monday-Sunday: 24-hour Service

Post time: Jul-22-2025