Structural Steel Pipe: Grades, Sizes and Applications Guide

Structural steel pipe is one of the most versatile products in any steel inventory. It carries loads, transfers forces, resists bending and torsion — and appears in everything from building frames and bridges to machinery, racks and handrails.

If you are sourcing structural steel pipe for a project, this guide explains the two main shapes (round and rectangular), the grades you will encounter, the size ranges that matter, and how to buy it efficiently — including from overseas suppliers.

Round vs Rectangular: Which Structural Pipe Do You Need?

Structural steel pipe comes in two main cross-section families:

Round structural pipe (circular hollow sections)

Round pipe is the most common structural shape. It offers:

• Uniform strength in all directions — ideal for columns, posts, bracing and members subject to loads from any angle;
• Excellent torsional resistance compared with open sections;
• Good bending characteristics for curved or welded frames.

Round structural pipe is specified by outer diameter × wall thickness (e.g., 48.3 × 3.2 mm, or in inches such as 2″ Schedule 40).

Rectangular and square HSS (hollow structural sections)

Rectangular and square pipe are used where flat surfaces make connections easier:

• Flat faces simplify bolted and welded connections to beams, gussets and plates;
• Higher stiffness in one axis for beams and lintels;
• A clean, architectural look popular in exposed structural and furniture applications.

Rectangular HSS is specified by width × height × wall thickness (e.g., 100 × 50 × 4 mm).

How to choose: use round pipe for columns and members loaded from any direction; use rectangular/square HSS for beams, frames and applications where flat connecting faces help.

Common Grades of Structural Steel Pipe

Structural pipe is specified to national standards, in the same families as structural plate:

Standard	Grade	Typical use
EN 10219	S235JRH / S275J0H / S355J2H	Cold-formed welded structural hollow sections (common in Europe)
EN 10210	S235JRH / S355J2H	Hot-finished structural hollow sections
ASTM	A500 Grade B / C	Cold-formed welded & seamless carbon steel HSS (common in North America)
ASTM	A53 Grade B	Welded and seamless steel pipe for general and structural use
JIS	G3466 STKR400 / STKR490	Carbon steel tubes for general structure (Asia-Pacific)
GB	Q235B / Q355B	Carbon structural steel pipe (China)

For most structural applications, Q235B / S235JRH / A500 Grade B / STKR400 sit in the same strength family (~235–275 MPa yield), while Q355B / S355J2H / A500 Grade C / STKR490 provide higher strength (~355 MPa) — useful for reducing member weight in heavier structures.

Buying tip: always confirm the standard + grade + dimensions (e.g., “EN 10219 S355J2H, 100×50×4mm, 6m lengths”). A grade name alone is not a complete specification.

Size Ranges and What They Mean

Structural steel pipe is available in a wide size range:

• Round pipe: outer diameters from about 21 mm to over 500 mm, wall thicknesses from 2 mm to over 20 mm;
• Rectangular HSS: from small sections like 40 × 20 mm up to large sections of 400 × 200 mm and beyond;
• Lengths: standard 6 m and 12 m lengths, or custom cut lengths.

When specifying, remember that structural pipe is weight-billed: the cost is per tonne, and the weight depends on diameter, wall thickness and length. A larger diameter or thicker wall increases both strength and cost — so don’t oversize members that only need light duty.

Where Structural Steel Pipe Is Used

• Building structures: columns, trusses, bracing and space frames;
• Bridges and walkways: main chords, cross-bracing and railings;
• Machinery and equipment: frames, legs, rollers and conveyor supports;
• Storage racks and platforms: posts, beams and guardrails;
• Signage and masts: flag poles, light poles and sign structures;
• Furniture and fittings: table frames, shelving and architectural details;
• Transportation: vehicle frames and trailers.

Buying Structural Steel Pipe: Practical Checklist

1. Specify standard + grade + size + length — four things, all mandatory for a usable quote;
2. Confirm the surface condition — mill finish, or painted/primed for exposed applications;
3. Ask about end finish — plain cut ends, beveled, or with protective caps for shipment;
4. Check the mill test certificate — verify grade and chemistry before acceptance;
5. Consider processing — cutting to length, drilling, welding and fabrication done at the supplier reduces your own handling;
6. Plan the logistics — pipe ships efficiently by container when bundled and strapped correctly.

Source Pipe and Steel from One Factory

SteelGuang supplies structural steel pipe in both round and rectangular/square HSS, in carbon structural grades (Q235B, Q355B, S235JRH/S355J2H, A500, STKR400/490 equivalents), together with steel plate, wear plate and boiler plate.

As a self-owned factory we can also cut, drill, weld and fabricate pipe to your drawing — so your order arrives as finished components, not just stock. Request a structural pipe quotation or see our steel pipe products. Send your standard, grade and sizes and we will confirm supply, MOQ and freight within 24 hours.

Summary

• Round pipe = uniform strength in all directions; rectangular/square HSS = flat connecting faces and one-axis stiffness.
• Common grades: S235JRH / S355J2H (EN), A500 B/C (ASTM), STKR400/490 (JIS), Q235B/Q355B (GB).
• Specify standard + grade + size + length; confirm the MTC; consider buying pre-processed from an integrated supplier.