Comprehensive Analysis of Square Pipe Hollow Sections

Comprehensive Analysis of Square Pipe Hollow Sections
Introduction

Square Pipe Hollow Sections (SHS), also referred to as square tubes or box sections, are structural steel profiles with a hollow, square cross-section. These sections are widely utilized in industries such as construction, machinery, rack systems, and container manufacturing due to their high strength-to-weight ratio, torsional rigidity, and aesthetic appeal. Their box-shaped configuration provides superior strength and rigidity compared to angles or channels, making them ideal for structural applications where loads are applied in multiple directions. This report provides an in-depth analysis of square pipe hollow sections, focusing on their specifications, standards, chemical composition, material properties, equivalent materials, and pipe sizes, with a scientific comparison of relevant data.

Square hollow sections are manufactured to meet various international standards, including ASTM A500, ASTM A53, EN 10210, EN 10219, JIS G 3466, BS 1387, and BS 6323. These standards ensure consistency in dimensions, mechanical properties, and chemical composition, making SHS suitable for diverse applications. The materials used, such as S235JR, S355JR, S275JR, C350LO, C250LO, G250, and G350 (C450LO), are selected based on their mechanical properties, weldability, and corrosion resistance. This report will explore these aspects in detail, supported by tables and comparative analyses.
Specifications
Outer Diameter

Square hollow sections are available in a wide range of outer diameters (OD), typically measured as the side length of the square cross-section. The OD ranges from 20 x 20 mm to 1200 x 1200 mm, accommodating various structural and industrial requirements. Smaller sizes (e.g., 20 x 20 mm) are used in lightweight applications like furniture or decorative structures, while larger sizes (e.g., 1200 x 1200 mm) are employed in heavy-duty construction, such as bridges or high-rise buildings.
Thickness

The wall thickness of square hollow sections varies from 2 mm to 20 mm (specifically 2, 3, 4, 5, 6, 8, 10, 12, 14, 16, 18, and 20 mm). The thickness directly influences the section’s strength, weight, and load-bearing capacity. Thicker walls provide higher strength but increase weight, while thinner walls are lighter but may have reduced load capacity.
Length

Standard lengths for square hollow sections are typically 5 meters, but customized lengths are available up to 18 meters depending on manufacturer capabilities and project requirements. Custom lengths are particularly useful in construction projects where precise dimensions are needed to minimize waste and fabrication costs.
Standard

Square hollow sections comply with multiple international standards, ensuring quality and performance:

ASTM A500: Covers cold-formed welded and seamless carbon steel structural tubing in rounds and shapes (Grades A, B, C, D).


ASTM A53: Specifies seamless and welded black and hot-dipped galvanized steel pipe.


EN 10210: Governs hot-finished structural hollow sections of non-alloy and fine-grain steels (e.g., S235JRH, S355J2H).


EN 10219: Applies to cold-formed welded structural hollow sections of non-alloy and fine-grain steels (e.g., S235JRH, S275JOH).


JIS G 3466: Japanese standard for carbon steel square and rectangular tubes for general structure.


BS 1387: British standard for screwed and socketed steel tubes.


BS 6323: Specifies seamless and welded steel tubes for automobile, mechanical, and general engineering purposes.
Technique

Square hollow sections are manufactured using various techniques:

Hot Rolled/Hot Expanded: Involves heating steel to form the hollow section, resulting in a uniform microstructure and improved mechanical properties.


Cold Rolled: Provides precise dimensions and a smooth surface finish, suitable for applications requiring high tolerances.


Electric Resistance Welded (ERW)/High Frequency Welded: Common for welded sections, offering cost-effectiveness and consistent quality.


Seamless: Produced without welds, seamless sections offer superior strength and are used in high-pressure or critical applications.


Annealed (Welded): Heat treatment to relieve stresses in welded sections, enhancing ductility and toughness.
Surface

The surface finish of square hollow sections can be customized based on application:

Black Bared: Uncoated steel, suitable for indoor or non-corrosive environments.


Galvanized: Coated with zinc (60–400 g/m²) for corrosion resistance, ideal for outdoor or marine applications.


Oiled/Painted/Powdered: Additional protective coatings to enhance durability and aesthetics.
Grade (ASTM/UNS)

Common grades include:

S235JR, S355JR, S275JR: European grades with varying yield strengths (235–355 N/mm²).


C350LO, C250LO: Australian grades with low-temperature impact properties.


G250, G350 (C450LO): High-strength grades for structural applications.


ASTM Grades: A500 (Gr. A, B, C, D), A53 (Gr. A, B), and others like SS400, STK500.
Chemical Composition

The chemical composition of square hollow sections varies by grade, influencing their mechanical properties and weldability. Below is a table summarizing the chemical composition of key grades:


Grade

C (max %)

Mn (max %)

P (max %)

S (max %)

Si (max %)

Other Elements


S235JR

0.17–0.20

1.40

0.040

0.040

-

Nb: 0.009 (max)


S275JR

0.21

1.50

0.040

0.040

-

-


S355JR

0.24

1.60

0.040

0.040

0.55

-


C250LO

0.12

1.30

0.030

0.030

0.25

-


C350LO

0.20

1.60

0.030

0.030

0.55

-


G250

0.12

1.30

0.030

0.030

0.25

-


G350 (C450LO)

0.20

1.60

0.030

0.030

0.55

-

Analysis

Carbon (C): Lower carbon content (e.g., 0.12% in C250LO) enhances weldability and ductility, while higher carbon (e.g., 0.24% in S355JR) increases strength but may reduce weldability.


Manganese (Mn): Improves strength and toughness; higher Mn in S355JR (1.60%) contributes to its higher yield strength.


Phosphorus (P) and Sulfur (S): Kept low to prevent brittleness and improve weldability.


Silicon (Si): Enhances strength and elasticity, particularly in S355JR and C350LO.
Material Properties

The mechanical properties of square hollow sections determine their suitability for specific applications. Below is a table summarizing key properties:


Grade

Yield Strength (N/mm²)

Tensile Strength (N/mm²)

Elongation (min %)

Impact Energy (J, at 0°C)


S235JR

235

360–510

26

27


S275JR

275

410–560

23

27


S355JR

355

470–630

22

27


C250LO

250

320–460

22

27 (at -20°C)


C350LO

350

430–550

20

27 (at -20°C)


G250

250

320–460

22

-


G350 (C450LO)

350

430–550

20

-

Analysis

Yield Strength: S355JR offers the highest yield strength (355 N/mm²), making it suitable for high-load applications. C250LO and G250 have lower yield strengths (250 N/mm²), ideal for lighter structures.


Tensile Strength: S355JR’s higher tensile strength (470–630 N/mm²) provides greater resistance to deformation under tension.


Elongation: Higher elongation in S235JR (26%) indicates better ductility, while S355JR’s lower elongation (22%) reflects its higher strength but reduced ductility.


Impact Energy: LO grades (C250LO, C350LO) are designed for low-temperature applications, offering good toughness at -20°C.
Equivalent Materials

Equivalent materials allow for substitution across standards, ensuring compatibility in global projects. Below is a table of equivalent grades:


Grade

EN Equivalent

ASTM Equivalent

JIS Equivalent

AS/NZS Equivalent


S235JR

EN 10025-2

ASTM A36

SS400

G250


S275JR

EN 10025-2

ASTM A572 Gr. 42

SS490

C250LO


S355JR

EN 10025-2

ASTM A572 Gr. 50

SM490A

C350LO


C250LO

S275JOH (EN 10210)

ASTM A500 Gr. B

STK400

G250


C350LO

S355J2H (EN 10210)

ASTM A500 Gr. C

STK490

G350


G250

S235JRH (EN 10219)

ASTM A500 Gr. A

SS400

C250LO


G350 (C450LO)

S355J2H (EN 10210)

ASTM A500 Gr. C

SM490A

C350LO

Analysis

S235JR: Equivalent to ASTM A36 and JIS SS400, widely used for general structural purposes due to its balance of strength and cost.


S355JR: Matches ASTM A572 Gr. 50, offering higher strength for demanding applications like bridges and heavy machinery.


C250LO/C350LO: Australian grades align with EN 10210 standards, suitable for low-temperature environments.
Pipe Sizes

Square hollow sections are available in a wide range of sizes to meet diverse application needs. The following table summarizes the size range:


Parameter

Range


Outer Diameter (OD)

20 x 20 mm to 1200 x 1200 mm


Wall Thickness

2, 3, 4, 5, 6, 8, 10, 12, 14, 16, 18, 20 mm


Length

5 m (standard), up to 18 m (customized)

Dimensional Tolerances

OD Tolerance: For pipes over 10 inches, ±1% of OD. For smaller sizes, typically ±0.5 mm.


Wall Thickness Tolerance: ±10% for welded pipes, ±3% for high-precision manufacturers.


Length Tolerance: -0 mm / +6 mm for definite cut lengths.


Squareness: Adjacent sides may deviate from 90° by ±2° for structural sizes.
Detailed Analysis and Comparison
Manufacturing Techniques

The choice of manufacturing technique impacts the performance and cost of square hollow sections:

Hot Rolled: Offers a uniform microstructure, ideal for structural applications requiring high strength. However, it may have slightly less precise dimensions compared to cold-rolled sections.


Cold Rolled: Provides tighter tolerances and a smoother surface, suitable for aesthetic or precision applications. It is less strong than hot-rolled sections due to work hardening.


Seamless vs. Welded: Seamless sections are stronger and more resistant to pressure but are more expensive. Welded sections (ERW or high-frequency welded) are cost-effective and sufficient for most structural applications.
Mechanical Properties Comparison

Comparing the mechanical properties of S235JR, S275JR, and S355JR:

S235JR: Offers moderate strength (235 N/mm² yield) and high ductility (26% elongation), making it cost-effective for general construction.


S275JR: Balances strength (275 N/mm² yield) and ductility (23% elongation), suitable for machinery and structural frames.


S355JR: Provides the highest strength (355 N/mm² yield) but lower ductility (22% elongation), ideal for heavy-duty applications like bridges.
Corrosion Resistance

Galvanized square hollow sections (zinc coating: 60–400 g/m²) offer superior corrosion resistance compared to black bared sections. For example, S355JR with galvanization is widely used in marine or outdoor environments, while uncoated S235JR is better suited for indoor applications.
Applications

Square hollow sections are versatile due to their structural efficiency:

Industrial Construction: Used in columns, beams, and frameworks due to high torsional resistance.


Machinery: Employed in equipment frames and supports, leveraging their rigidity.


Rack Systems: Ideal for storage racks due to their uniform strength and ease of assembly.


Container Manufacturing: Used in container frames for their strength and lightweight properties.
Scientific Comparison

To scientifically compare the grades, consider their performance under load:

Load-Bearing Capacity: S355JR’s higher yield strength (355 N/mm²) allows it to support greater loads than S235JR (235 N/mm²). For a 100 x 100 x 5 mm SHS, S355JR can support approximately 50% more load before yielding.


Weight Efficiency: For the same load, S355JR requires a thinner wall thickness than S235JR, reducing material costs and weight.


Weldability: Lower carbon content in C250LO (0.12%) makes it easier to weld than S355JR (0.24%), reducing the need for preheating.
Practical Considerations
Delivery and Packing

Delivery: Typically within 30 days, depending on order quantity and customization.


Packing: Waterproof paper wrapping and steel strip bundling ensure protection during transport. Two tags per bundle provide traceability.
Ends

Square Cut/Threaded: Ensures compatibility with fittings or connections.


Burr Removed: Enhances safety and ease of handling during installation.
Cost Analysis

S235JR: Most cost-effective due to lower strength and simpler manufacturing.


S355JR: Higher cost due to enhanced mechanical properties and alloying elements.


Galvanized Sections: Additional coating increases costs but extends service life in corrosive environments.
Conclusion

Square pipe hollow sections are critical components in modern construction and engineering, offering a balance of strength, versatility, and cost-effectiveness. Standards like ASTM A500, EN 10210, and JIS G 3466 ensure quality and consistency across applications. Grades such as S235JR, S275JR, and S355JR cater to varying strength and ductility needs, while Australian grades like C250LO and C350LO provide low-temperature performance. The choice of manufacturing technique, surface finish, and size depends on the specific application, with seamless sections offering superior strength and welded sections providing cost savings. By understanding the chemical composition, mechanical properties, and equivalent materials, engineers can select the optimal SHS for their projects, ensuring safety, durability, and efficiency.