Seamless steel pipes are mainly used to manufacture high-pressure and above pressure steam boiler pipes made of high-quality carbon structural steel, alloy structural steel, and stainless heat-resistant steel seamless pipes. These boiler pipes work under high temperature and high pressure conditions. The pipes will also oxidize and corrode under the action of high-temperature flue gas and water vapor. Therefore, it is required that the steel pipe has high durability strength, high oxidation resistance, and good structural stability. The adopted steel grades include: high-quality carbon structural steel grades such as 20G, 20MnG, 25MnG; alloy structural steel grades such as 15MoG, 20MoG, 12CrMoG, 15CrMoG, 12Cr2MoG, 12CrMoVG, 12Cr3MoVSiTiB; rust-resistant heat-resistant steel commonly uses 1Cr18Ni9, 1Cr18Ni11Nb. In addition to ensuring chemical composition and mechanical properties, high-pressure boiler pipes must undergo hydrostatic testing on each piece, and must undergo expansion and flattening tests. High-pressure seamless pipes are delivered in a heat-treated state.
Standardized external diameter allowable deviation for high-pressure pipes:
D1 ±1.5%, minimum ±0.75 mm
D2 ±1.0%, minimum ±0.50 mm
D3 ±0.75%, minimum ±0.30 mm
D4 ±0.50%, minimum ±0.10 mm
Weight calculation formula for high-pressure pipes:
[(Outer Diameter - Wall Thickness) * Wall Thickness] * 0.02466 = kg/m (weight per meter)
GB5310-2008 "High-pressure Boiler Seamless Steel Pipes" specifies that the outer diameter of hot-rolled pipes ranges from 22 to 530mm, with wall thicknesses ranging from 20 to 70mm. For cold-drawn (cold-rolled) pipes, the outer diameter ranges from 10 to 108mm, with wall thicknesses ranging from 2.0 to 13.0mm.