Q345 welded steel pipe is a high-strength, low-alloy structural steel pipe manufactured by forming and welding Q345 steel plates or coils. It is one of the most widely used grades in China, conforming to the GB/T 1591 standard (equivalent to the European EN 10025-2 S355 grade). The designation "Q345" signifies that the material's yield strength (σs) is 345 MPa minimum. Its excellent combination of strength, toughness, weldability, and cost-effectiveness makes it a fundamental material across numerous heavy-duty industrial and construction applications.

Key Material Properties

The properties of Q345 steel are the foundation of the pipe's performance:

High Yield Strength: The minimum yield strength of 345 MPa provides superior load-bearing capacity compared to common carbon steels like Q235, allowing for structures that are stronger yet lighter.

Good Toughness and Ductility: Q345 offers good impact toughness, even at lower temperatures, which helps prevent brittle fracture under stress or dynamic loading.

Excellent Weldability: The chemical composition of Q345, with controlled amounts of carbon, manganese, silicon, and microalloying elements like vanadium and niobium, makes it highly suitable for all common welding techniques without pre-heating in most cases. This ensures strong, integral weld joints.

Atmospheric Corrosion Resistance: As a low-alloy steel, Q345 exhibits better resistance to atmospheric corrosion than standard carbon steel.

Manufacturing Process

Q345 Welded pipes are produced through two primary methods:

ERW (Electric Resistance Welding): Steel coil is uncoiled, formed into a cylindrical shape through a series of rolls, and its edges are heated and fused together using high-frequency electrical current. This is a high-efficiency process ideal for large-volume production of pipes with small to medium diameters.

SAW (Submerged Arc Welding): For larger diameter and thicker-walled pipes, SAW is preferred. Pre-formed steel plates are welded along the seam (straight seam: LSAW; or spiral seam: SSAW) under a layer of flux, which prevents atmospheric contamination and creates deep, high-integrity welds.

After welding, the pipes often undergo sizing, non-destructive testing (like ultrasonic or X-ray inspection), and various finishing treatments.

Applications

Q345 Welded pipes are renowned for their versatility and are employed in a vast array of sectors:

Structural and Construction: Building frames, bridges, transmission towers, and support columns in high-rise buildings and large industrial facilities.

Oil and Gas Industry: For structural parts, fluid transportation pipelines (onshore and offshore), and framework for drilling platforms.

Mechanical and Heavy Equipment: As components in agricultural machinery, mining equipment, and material handling systems.

Infrastructure Projects: Piling, foundation support, and scaffolding.

Automotive and Transportation: For chassis parts and roll cages in heavy-duty vehicles.