Q355GNH low-alloy structural steel pipe, Steel plates for high-rise buildings have the properties of easy welding, earthquake resistance, and low-temperature impact resistance, and are mainly used in large-scale projects such as high-rise buildings, super-tall buildings, large-span stadiums, airports, exhibition centers, and steel structure workshops.
Compared with ordinary Q235B / Q345B steel pipe, these plates for high-rise buildings have upper limits on yield strength and improved tensile strength, and have requirements for carbon equivalent and yield ratio indexes.
Q355GNH straight seam welded steel pipe
A Q355GNH steel plate that meets the GB/T 1591–2018 standard is selected as the raw material to ensure that its chemical composition and mechanical properties meet the requirements. The typical chemical composition includes C <= 0.12%, Mn 0.20–1.60%, Si 0.25–1.00%, and Cu 0.20–0.50%. The yield strength is >=355 MPa, and tensile strength is 470–630 MPa, ensuring excellent forming and welding performance.
The steel plate is pretreated by leveling, cutting, planing, and edge milling to ensure dimensional accuracy and surface quality.
Plate thickness: 4–25 mm
Width tolerance: ±0.5 mm
Surface roughness (Ra): <=3.2 μm
The steel plate is rolled into a tube by a forming machine to create the prototype of the straight seam welded pipe. The forming process uses roll forming or UOE (U-ing, O-ing, and Expansion) technology depending on pipe diameter.
Applicable outer diameter range: Φ219–Φ2020 mm
Roundness deviation: <=1% of the outer diameter
Use High-Frequency Welding (HFW) or Submerged Arc Welding (SAW) to join the edges of the steel plates and form a continuous welded pipe.
High-Frequency Welding (HFW):
Utilizes the skin effect and proximity effect generated by high-frequency current to heat the edges of the steel plates to the melting point, achieving pressure welding.
Frequency: 300–500 kHz
Welding current: 600–1200 A
Welding speed: 10–60 m/min
Suitable for: small and medium-diameter pipes (Φ50–Φ610 mm)
The arc burns beneath a layer of flux, melting the base metal and filler to form a high-quality weld.
Welding current: 500–1000 A
Voltage: 28–36 V
Heat input: 25–40 kJ/cm
Suitable for: large-diameter and thick-walled pipes (Φ610–Φ2020 mm)
After welding, internal and external burrs are removed using a trimming or milling machine. The weld is then polished to achieve a smooth surface.
Internal bead height: <=0.5 mm
External bead height: <=1.0 mm
Surface flatness deviation: <=0.3 mm/m
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