Galvanized Steel Hollow Section

Galvanized Steel Hollow Section Overview

Galvanized steel hollow sections are structural steel tubes coated with a layer of zinc to enhance corrosion resistance. They are widely used in construction, infrastructure, automotive, and industrial applications due to their durability, strength, and versatility. The materials specified—Gr.A, Gr.B, Gr.C, S275J0H, S355JR, S355J0H, S355J2H, A36, SS400, Q195, Q235, and Q345—comply with various international standards such as ASTM A500, ASTM A53, API 5L, BS1387, EN39, JIS 3466, EN10219, and GB/T 13793-1992. These standards define the mechanical properties, chemical composition, and manufacturing processes for hollow sections, ensuring they meet specific performance criteria.

This document provides an in-depth analysis of the galvanizing processes (hot-dip and cold), forming techniques, specifications, quality inspection methods, and processing details for round, rectangular, and square galvanized steel pipes.

Materials and Standards

Table 1: Material Grades and Corresponding Standards

Material Grade	Standard	Description
Gr.A, Gr.B, Gr.C	ASTM A500, ASTM A53	Carbon steel grades with varying tensile and yield strengths for structural use
S275J0H	EN10219	Structural steel with minimum yield strength of 275 MPa, cold-formed
S355JR	EN10219	Higher strength steel (355 MPa yield), suitable for structural applications
S355J0H	EN10219	Cold-formed structural steel with 355 MPa yield strength
S355J2H	EN10219	Enhanced toughness steel for low-temperature applications
A36	ASTM A36	Low carbon steel with good weldability and formability
SS400	JIS G3101	General-purpose structural steel, equivalent to mild steel
Q195	GB/T 13793-1992	Low carbon steel with basic strength, used in light structural applications
Q235	GB/T 13793-1992	Mild steel with moderate strength, widely used in construction
Q345	GB/T 13793-1992	High-strength low-alloy steel, equivalent to S355 grades

Material Properties

Gr.A, Gr.B, Gr.C (ASTM A500): These grades differ in yield strength (e.g., Gr.A: 230 MPa, Gr.B: 315 MPa, Gr.C: 345 MPa) and are used for structural tubing.
S275J0H, S355JR, S355J0H, S355J2H (EN10219): European grades with specified impact toughness and yield strengths, ideal for hollow sections.
A36: Yield strength of 250 MPa, commonly used in the U.S. for structural purposes.
SS400: Yield strength of 245 MPa, a Japanese standard steel with excellent ductility.
Q195, Q235, Q345: Chinese grades with increasing strength (Q195: 195 MPa, Q235: 235 MPa, Q345: 345 MPa).

Standards Overview

ASTM A500: Specifies cold-formed welded and seamless carbon steel structural tubing.
ASTM A53: Covers seamless and welded steel pipes, often galvanized for corrosion resistance.
API 5L: Standards for line pipes, applicable to oil and gas industries.
BS1387: British standard for welded steel tubes, often galvanized.
EN39: Specifies steel tubes for scaffolding.
JIS 3466: Japanese standard for rectangular structural steel tubes.
EN10219: European standard for cold-formed welded structural hollow sections.
GB/T 13793-1992: Chinese standard for welded steel pipes.

Galvanizing Processes

Galvanizing is the process of applying a zinc coating to steel to prevent corrosion. Two primary methods are used: hot-dip galvanizing and cold galvanizing.

Hot-Dip Galvanizing

Hot-dip galvanizing involves immersing steel in a bath of molten zinc at approximately 450°C (842°F). This process creates a metallurgically bonded zinc-iron alloy layer, providing robust corrosion protection.

Process Steps:
1. Surface Preparation: Steel is cleaned via degreasing, pickling (acid bath), and fluxing (zinc ammonium chloride solution) to remove rust, oil, and impurities.
2. Immersion: The cleaned steel is dipped into molten zinc, typically at 440-460°C.
3. Cooling: The coated steel is withdrawn and cooled in air or water, forming a crystalline zinc surface.
4. Inspection: Coating thickness and uniformity are checked.
Coating Thickness: Typically ranges from 40-600 g/m² (depending on standards and requirements), equivalent to 5-85 µm per side.
Advantages:
- Thick, durable coating with excellent corrosion resistance.
- Self-healing properties due to zinc’s sacrificial anodic behavior.
Disadvantages:
- Higher cost and energy consumption.
- Potential for uneven coating on complex shapes.

Cold Galvanizing

Cold galvanizing involves applying a zinc-rich paint or coating to the steel surface, typically via spraying, brushing, or dipping. The zinc content in the coating is usually 90-95%.

Process Steps:
1. Surface Preparation: Steel is cleaned to remove dirt, grease, and rust (e.g., sandblasting to Sa2.5 standard).
2. Application: Zinc-rich paint is applied using a spray gun, brush, or roller.
3. Curing: The coating dries at ambient temperature, forming a protective layer.
4. Inspection: Coating adhesion and thickness are verified.
Coating Thickness: Typically 20-80 µm, thinner than hot-dip galvanizing.
Advantages:
- Lower cost and simpler application.
- Suitable for on-site repairs or small components.
Disadvantages:
- Less durable than hot-dip galvanizing.
- No metallurgical bonding, reducing long-term corrosion resistance.

Table 2: Comparison of Hot-Dip and Cold Galvanizing

Parameter	Hot-Dip Galvanizing	Cold Galvanizing
Zinc Application	Molten zinc bath	Zinc-rich paint
Coating Thickness	40-600 g/m² (5-85 µm/side)	20-80 µm
Bonding	Metallurgical (zinc-iron alloy)	Mechanical (paint adhesion)
Corrosion Resistance	High	Moderate
Cost	Higher	Lower
Application	Factory-based	On-site or factory
Durability	20-50 years	5-15 years

Forming Process

The forming process for galvanized steel hollow sections varies depending on whether the section is seamless or welded and its shape (round, rectangular, or square).

Seamless Hollow Sections

Process:
1. Billet Preparation: A solid steel billet (e.g., Q235 or S355JR) is heated to 1200-1300°C.
2. Piercing: The billet is pierced using a mandrel to form a hollow tube.
3. Rolling: The tube is elongated and shaped via hot rolling.
4. Sizing: Final dimensions are achieved through cold drawing or sizing rolls.
Standards: ASTM A53, API 5L.
Advantages: Higher strength and no weld seam weaknesses.

Welded Hollow Sections

Process:
1. Strip Preparation: Steel coils (e.g., SS400 or Q345) are slit into strips.
2. Forming: Strips are cold-formed into a round shape using rollers (ERW process) or bent into rectangular/square shapes (JIS 3466).
3. Welding: Edges are welded using high-frequency electric resistance welding (ERW) or submerged arc welding (SAW).
4. Shaping: For rectangular/square sections, the round tube is further formed into the desired shape.
5. Galvanizing: Applied post-forming (hot-dip) or pre-galvanized strips are used.
Standards: ASTM A500, EN10219, BS1387.
Advantages: Cost-effective and suitable for mass production.

Pre-Galvanized vs. Post-Galvanized Forming

Pre-Galvanized: Steel strips are galvanized before forming. Weld seams may lack zinc coating unless touched up.
Post-Galvanized: Entire section is galvanized after forming, ensuring uniform coating.

Specifications

Table 3: Specifications for Galvanized Steel Hollow Sections

Parameter	Round Pipe	Rectangular Pipe	Square Pipe
Outer Diameter (OD)	12.7-609 mm	N/A	N/A
Width x Height	N/A	10×15 to 800×1200 mm	10×10 to 1200×1200 mm
Wall Thickness (WT)	0.5-60 mm	0.5-60 mm	0.5-60 mm
Length	0.5-26.5 m (customizable)	0.5-26.5 m (customizable)	0.5-26.5 m (customizable)
Zinc Coating	40-600 g/m²	40-600 g/m²	40-600 g/m²
Standards	ASTM A500, A53, BS1387	EN10219, JIS 3466	EN10219, JIS 3466

Tolerances:
- OD: ±1% (ASTM A500).
- WT: ±10% (EN10219).
- Length: ±50 mm or as specified.

Quality Inspection

Quality inspection ensures galvanized steel hollow sections meet structural and corrosion resistance requirements.

Methods

Visual Inspection:
- Check for surface defects (cracks, dents) and zinc coating uniformity.
Coating Thickness Test:
- Magnetic gauge or micrometer to measure zinc thickness (e.g., ASTM A123 requires 45-85 µm for structural steel).
Dimensional Check:
- Verify OD, WT, length, and straightness using calipers, rulers, or laser systems.
Mechanical Testing:
- Tensile test (yield strength, elongation per ASTM A500).
- Bend test (ductility).
Corrosion Resistance:
- Salt spray test (ASTM B117) to assess zinc coating durability.
Weld Integrity:
- Ultrasonic testing (UT) or X-ray for welded sections.

Table 4: Quality Inspection Standards

Test	Standard	Requirement
Zinc Coating Thickness	ASTM A123	40-600 g/m² (varies by thickness)
Tensile Strength	ASTM A500	Gr.B: 315 MPa min
Yield Strength	EN10219	S355J2H: 355 MPa min
Weld Seam	BS1387	No visible cracks or porosity
Corrosion Test	ASTM B117	500-1000 hours without red rust

Galvanized Pipe Processing Process

Steps

Raw Material Selection: Choose appropriate steel grade (e.g., Q235, S355JR).
Forming: Seamless or welded process to create hollow sections.
Galvanizing: Hot-dip or cold galvanizing applied.
Cutting: Pipes cut to specified lengths using saws or plasma cutters.
End Finishing: Plain ends, beveled (30-35°), or threaded (BS1387).
Surface Treatment: Optional painting or additional coatings (e.g., 3LPE).
Packaging: Bundled or crated for transport.

Round Galvanized Steel Pipe

Applications: Water supply, gas pipelines, scaffolding (BS1387, EN39).
Sizes: OD 12.7-609 mm, WT 0.5-60 mm.
Features: High pressure resistance, easy threading.
Processing: Often ERW welded, then hot-dip galvanized.

Rectangular Galvanized Steel Pipe

Applications: Structural frameworks, fencing, furniture (EN10219, JIS 3466).
Sizes: 10×15 to 800×1200 mm, WT 0.5-60 mm.
Features: High load-bearing capacity in one direction.
Processing: Formed from round tubes, galvanized post-forming.

Square Galvanized Steel Pipe

Applications: Building columns, machinery frames (EN10219, JIS 3466).
Sizes: 10×10 to 1200×1200 mm, WT 0.5-60 mm.
Features: Uniform strength in all directions.
Processing: Similar to rectangular, with precise corner radii.

Conclusion

Galvanized steel hollow sections, made from materials like Gr.A, Gr.B, Gr.C, S275J0H, S355JR, S355J0H, S355J2H, A36, SS400, Q195, Q235, and Q345, adhere to standards such as ASTM A500, ASTM A53, API 5L, BS1387, EN39, JIS 3466, EN10219, and GB/T 13793-1992. The choice between hot-dip and cold galvanizing, seamless or welded forming, and specific shapes (round, rectangular, square) depends on application requirements. Rigorous quality inspection ensures compliance with mechanical and corrosion resistance standards, making these products reliable for diverse uses.

Galvanized Steel Pipe | Hot-dip and Cold-dip Galvanized Steel

As a professional manufactrer of steel products, we focus on the production of high-frequency welded pipes, galvanized steel pipes and scaffolding products. Also other steel products can supplied by our trading company such as Longitudinally Submerged Arc Welding and Spiral Submerged Arc Welding tube,API Line pipe

Hot Dipped Galvanized Steel Scaffold Pipe

ASTM A53/BS1387 Hot DIP Galvanized Round Steel Pipe for Scaffolding Tube

pre-galvanized components are usually only immersed in the galvanizing bath for a very short time, resulting in a relatively thin coating. The thicker zinc coating produced by hot dip galvanization offers improved rust and corrosion protection versus pre-galvanization.

Zinc Coated Galvanized Steel Pipe

Galvanized pipes have a wide range of uses. In addition to oil and other low-pressure fluid pipelines, it is also used as oil well pipes in the petroleum industry, especially in offshore oil fields, oil heaters in chemical coking equipment, coal distillation, and oil washing converter pipes, bridges, etc. Pipe pile, mining tunnel support frame with pipe, etc. Developed countries in the world started to develop new pipes and continuously banned galvanized pipes.

Schedule 40 black steel pipe

ASTM A53 black steel pipe, also referred to as ASME SA53 pipe, is an excellent candidate for most processing. Featuring a semi-smooth surface coated with black lacquer. Black steel pipe is intended for mechanical and pressure application. Common applications include steam, water, air, and gas systems. ASTM A53 is the standards specification covers seamless and welded, black and hot-dipped galvanized nominal (average) wall pipe for coiling, bending, flanging and other special purposes and is suitable for welding. A53 bare steel pipe sizes are specified by two non-dimensional numbers. Nominal pipe size (NPS) or inside dia

EN39 Galvanized Steel Pipe

Remember, EN39 galvanized steel pipes are a reliable and versatile choice for various applications. Their corrosion resistance, durability, and ease of installation make them an excellent option for construction projects and industrial applications.

Difference Between EN39 & BS1139 Galvanized Steel Pipe

EN39 and BS1139 are two different standards that govern the manufacturing and specifications of galvanized steel pipes. While both standards focus on galvanized steel pipes used in scaffolding applications, there are some key differences between EN39 and BS1139 galvanized steel pipes. In this article, we will explore these differences to help you understand which standard is most suitable for your specific requirements.