Black Square Hollow Section Tube Q235B Q345B SHS Steel Tube For Construction

Black Square Hollow Section (SHS) ERW Welded Steel Tube for Construction

Q235B / Q345B | Equivalent to ASTM A36 / A572 Gr.50 | EN S235JR / S355JR

Product Overview

Black Square Hollow Section (SHS) is an ERW welded steel tube supplied in uncoated, mill-finish condition. The term "Black" refers to the natural oxidized surface retained from the steel mill — it is not a painted or coated product. This is the base material from which all galvanized and painted square tubes are made.

The tube is produced by the ERW (Electric Resistance Welding) process, in which steel strip is cold-formed into a square section and the longitudinal seam is welded using high-frequency current. This is the mainstream production method for square hollow sections, offering high efficiency, consistent wall thickness, and precise dimensional accuracy.

Material Grades & International Equivalents

Notes on Equivalency:
These grades are approximate equivalents, not exact substitutes. Chemical composition and mechanical properties may differ slightly between standards. For export orders, mill test certificates can be issued showing the corresponding international grade designation upon request.

Surface Condition

Supplied in Black (uncoated) condition, typically with a light anti-rust oil applied at the mill for protection during transport and short-term storage. This surface is ideal for:

• Components to be painted, powder-coated, or hot-dip galvanized after fabrication

• Indoor structural frames, machinery bases, and welded assemblies

• Heavy fabrication where anti-corrosion treatment is applied after welding

Note: Black SHS is not intended for direct outdoor or moisture-exposed service. For outdoor applications, hot-dip galvanizing or painting after welding is recommended.

Size Range (Typical)

Standards

Manufactured to EN 10219, ASTM A500, GB/T 6728, or equivalent standards. Mill test certificates are available upon request.

Typical Applications

• Indoor building structural frames

• Machinery manufacturing and equipment bases

• Conveyor line supports and welded structural components

• Semi-finished parts requiring subsequent painting or galvanizing

• General construction and fabrication projects

Why Choose Black SHS ERW Welded Tube

• Cost-effective — lower unit price than galvanized or painted tube

• Fabrication-friendly — excellent weldability for cutting, drilling, and joining

• Versatile — suitable for a wide range of structural and mechanical applications

• Customizable — sizes, wall thicknesses, and lengths can be produced to order