Q345 Rectangular pipe, more accurately referred to as Q345 Rectangular Hollow Section (RHS) in international trade, is a type of cold-formed welded structural steel pipe with a rectangular cross-section. It is manufactured from Q345 grade steel, a high-strength low-alloy (HSLA) structural steel widely used in China. The designation "Q345" signifies that the material's yield strength (σs) is 345 MPa minimum.

Key Characteristics and Advantages

High Strength-to-Weight Ratio: Q345 steel offers significantly higher yield and tensile strength compared to common carbon steels like Q235. This allows for the design of lighter structures that can bear heavier loads, leading to material savings and cost efficiency.

Excellent Mechanical Properties: This grade possesses good ductility and toughness, ensuring it can withstand impact, bending, and vibration without brittle fracture. It also offers good weldability and formability.

Structural Efficiency: The rectangular shape provides a large moment of inertia and section modulus, making it exceptionally resistant to bending and torsion from multiple axes. This shape is ideal for connections and fabrications, as it offers flat surfaces for welding and bolting.

Aesthetic Appeal: The clean, linear appearance of rectangular hollow sections is often preferred in modern architectural designs for both structural and exposed aesthetic applications.

Manufacturing Process

Q345 RHS is typically produced through a cold-forming process. Steel strips (coils) of Q345 grade are uncoiled, guided through a series of forming rolls that gradually shape them into a closed circular tube. The edges are then welded together using high-frequency electric resistance welding (HFW/ERW). The welded tube is subsequently passed through a set of shaping rolls to transform it from a circular into a precise rectangular or square profile.

Applications

Q345 rectangular pipes are fundamental components in a vast array of industries due to their strength and versatility:

Construction and Building Structures: Widely used as columns, beams, trusses, and frameworks in industrial plants, high-rise buildings, commercial centers, and stadiums.

Machinery and Equipment Manufacturing: Used to build robust frames and bases for heavy machinery, agricultural equipment, and automated production lines.

Bridge Construction: Employed in the construction of bridge supports, girders, and pedestrian walkways.

Automotive and Transportation: Used in the chassis of buses, trucks, and trailers, as well as in material handling equipment like forklifts and cranes.

Architectural and Decorative Applications: Popular for modern architectural elements such as gates, fences, canopies, and interior design features due to its sleek appearance.

Available Specifications

Material Grade: Q345A, B, C, D, E (differing in impact toughness tested at different temperatures).

Standards: Produced according to Chinese standards GB/T 6728 (for cold-formed sections) and often compatible with international tolerances.

Sizes: Available in a wide range of dimensions, with outer widths and heights typically ranging from 20mm x 10mm to 500mm x 300mm and above. Wall thickness commonly ranges from 1.0mm to 16mm.