I. Structural seamless pipe material type and selection basis
Structural seamless pipe are widely made of carbon steel, low alloy high strength steel and special alloy steel, the specific material selection needs to match the application scenario:
(1) Carbon steel (e.g. 20#, Q345B): low cost, good weldability, suitable for construction brackets, machinery frames and other conventional structures.
(2) Low-alloy high-strength steel (e.g. ST52.3, ASTM A106 Gr.B): Strength is enhanced by adding elements such as manganese and silicon, and the tensile strength can reach more than 470MPa, which is suitable for high load scenarios such as bridges and heavy equipment.
(3) Stainless steel (e.g. 304, 316): high corrosion resistance, used in marine platforms or chemical environments.
II. Structural seamless pipe standards and grades
| Category | Standard | Common Grades | Common Foreign Standards |
|---|---|---|---|
| Structural Seamless Pipe | GB/T 8162-2008 | 10, 20, 35, 45, 40Mn2, 45Mn2, 27SiMn, 20Cr, 40Cr, 20CrMO, 35CrMO, 38CrMoAI, 50CrV, 30CrMnSi | ASTM A500-98, ASTM A501-98, ASTM A519-96, JISG3441-1988, JISG3444-1994 |
| Fluid Conveyance Seamless Pipe | GB/T 8163-2008 | 10, 20, 09MnV, 16Mn | ASTMA53-98, JISG3452-1988, JISG3454-1988, DINI629-1984 |
| Petroleum Casing | API SPEC 5CT | J55, K55, N80, P110, C75, L80, C90, C95, T95, L80S, N80T, V150 | - |
| Petroleum Tubing and Couplings | API SPEC 5CT | J55, N80, C90, T95, P110, M65, 80SS | - |
| Pipeline Steel Pipe | API SPEC 5L | A25, A, B, X42, X46, X52, X56, X60, X65, X70 | - |
| High-Pressure Boiler Seamless Pipe | GB 5310-2008 | 20G, 20MnG, 25MnG, 15MoG, 20MoG, 12CrlMoVG, 15CrMoG, 12Cr2MoG, 12Cr2MoWVTiB, 12Cr3MOVSiTiB | ASTMAI06-97a, ASTMA213-95a, JISG3461-1988, JISG3462-1988, DINI7175-1979, BS3059:Part2:1990 |
| Low-Medium Pressure Boiler Seamless Pipe | GB 3087-2008 | 10, 20 | - |
| Fertilizer Equipment High-Pressure Seamless Pipe | GB 6479-2013 | 10, 20G, 16Mn, 15MnV, 10MoWVNb, 12CrMO, 15CrMO, 1Cr5Mo, 12Cr2MO | 1S09329-2-1997, ASTMA161-94 |
| Petroleum Cracking Seamless Pipe | GB 9948-2013 | 10, 20, 12CrMO, 15CrMO, 1Cr2Mo, 1Cr5Mo | JISG3441-1988 |
| Automotive Semi-Axle Tube Seamless Pipe | YB/T 5053-1997 | 45Mn2, 45, 25Mn9, 40MnB | DINI629-1984 |
| Hydraulic Support Hot-Rolled Seamless Pipe | GB/T 17396-2009 | 27SiMn | DINI629-1984 |
| Shipbuilding Carbon Steel Seamless Pipe | GB/T 5312-2009 | C10, C20 | - |
| Cold-Drawn Precision Seamless Pipe | GB/T 3639-2009, GB/T 8162-2008 | 10, 20, 35, 45, 20CrMO | DIN2391-1994 |
| Geological Drilling Seamless Pipe | GB/T 4975-2012 | DZ40, DZ50 | - |
| Shell Case Seamless Pipe | YBn-86 | 40Mn2, D60 | - |
| Die Rod Seamless Pipe | Q/OHAD003-94 | 1Cr5MO | - |
| Bearing Steel Pipe | YB/Z 12-77YJZ84 | GCr5M0 | - |
| Reinforcing Bar Coupling Seamless Pipe | Q/0HAD011-1997a | 10, 20 | - |
| Cylinder Seamless Pipe | GB/T 18248-2008 | 34Mn2V, 30CrMO, 35CrMo, 45 | - |
III. Core Performance Advantages
Seamless pipe for structural use achieves the following properties through a complete structure without welded seams:
(1) High strength and uniformity: Hot rolled seamless pipes eliminate internal stresses through high temperature rolling, while cold-drawn seamless pipes enhance dimensional accuracy, both of which avoid the problem of weak weld seams in welded tubes.
(2) Pressure and impact resistance: seamless steel pipe with uniform wall thickness can withstand high pressure and dynamic loads, which is better than welded steel pipe that is prone to cracking.
(3) Processing adaptability: can be directly bending, flaring and other forming processes, without worrying about weld cracking.
(1) Structural integrity: seamless steel pipe has no welding seam, avoiding the risk of welding defects; welded steel pipe relies on the quality of the welding seam and requires additional flaw detection.
(2) Cost and Efficiency: Welded steel pipe has low production cost and high efficiency, and is suitable for large calibre or non-load-bearing structures; seamless pipe for structural use is more costly but has a longer lifespan and is suitable for critical load-bearing components.
(3) Size range: Hot rolled seamless pipe can produce large pipe diameters above Φ600mm, while welded steel pipe has higher size flexibility.
V. Hot rolling and cold drawing process differences
(1) Hot rolled seamless pipe: formed by rolling at high temperature, there is an oxidised layer on the surface but the production efficiency is high, suitable for thick-walled and large-diameter pipes (e.g. building columns).
(2) Cold-drawn seamless tubes: drawn and moulded at room temperature, with high dimensional accuracy (tolerance ±0.1mm) and smooth surface, suitable for precision mechanical parts (e.g. hydraulic cylinders).
VI. Application Scene Suitability
(1) Construction: Hot rolled seamless tubes are used for trusses and support columns to take advantage of their high loading capacity.
(2) Mechanical engineering: Cold-drawn seamless tubes are processed into shaft parts to ensure dimensional stability.
(3) Energy and transport: Low-alloy, high-strength steel seamless tubes are used in oil and gas pipelines and ship structures, balancing the need for strength and corrosion resistance.
VII. Structural seamless pipe specification size
Standard material: 20G 16Mn
Execution standard：GB5310-95、GB6479-86、GB9948-88
| 25×2.5-5 | 57×3-8 | 114×5-20 | 168×8-30 | 325×8-45 |
| 28×3-5 | 60×4-10 | 121×5-20 | 180×7-30 | 351×10-36 |
| 32×3-5 | 63.5×4-12 | 127×6-20 | 194×8-30 | 377×10-38 |
| 38×3-6 | 76×4-14 | 133×5-22 | 203×10-32 | 402×10-45 |
| 42×3-6 | 83×5-14 | 140×6-22 | 219×7-45 | 426×10-30 |
| 45×3-6 | 89×4.5-20 | 146×8-25 | 245×8-45 | 480×12-30 |
| 48×3-6 | 102×4-20 | 152×8-25 | 273×8-50 | 530×12-30 |
Medium and low pressure boiler pipe, fluid pipe, geological pipe standard material: 20# dz40
Execution standard: GB3087-1999, GB8163-1999, YB23-70
| 8×1-2 | 38×3-7 | 95×6-20 | 159×5-40 | 351×10-50 |
| 10×1-2 | 42×3-8 | 102×4-20 | 168×8-40 | 377×10-50 |
| 12×1-2.5 | 45×3-8 | 108×4-20 | 180×7-40 | 402×10-50 |
| 14×1.5-4 | 51×3-10 | 114×4-20 | 194×8-40 | 426×10-50 |
| 16×2-4 | 57×3-10 | 121×5-20 | 203×10-45 | 480×12-45 |
| 18×2-5 | 60×3-12 | 127×6-25 | 219×7-50 | 530×12-40 |
| 22×2-5 | 63.5×3-14 | 133×5-25 | 245×8-50 | 450×12-40 |
| 25×2-6 | 76×4-14 | 140×6-25 | 273×8-50 | 610×12-30 |
| 28×2-6 | 83×5-16 | 146×8-20 | 299×10-50 | 430×12-30 |
| 32×2.5-6 | 89×4-20 | 152×8-30 | 325×8-50 | 720×12-30 |
VIII. Structural seamless steel pipe size specifications
| Item | Value |
|---|---|
| Outer Diameter and Wall Thickness | Should comply with the provisions of GB/T17395 |
| Length |
1. Hot-rolled (extruded, expanded) steel tubes: 3~12m 2. Cold-drawn (rolled) steel tubes: 2~10.5m |
| Bowing |
1. When wall thickness ≤15mm, it shall not exceed 1.5mm/m 2. When wall thickness >15~30mm, it shall not exceed 2.0mm/m 3. When wall thickness >30mm or outer diameter ≥351mm, it shall not exceed 3.0mm/m |
IX. Permissible deviations of external diameter and wall thickness
| Steel Pipe Type | OD/WT | Dimension | Allowable deviation (normal) | Permissible deviation (advanced) |
|---|---|---|---|---|
| Hot-rolled (extruded, pressed) pipe | Outer Diameter | <50 | ± 0.50 mm | ± 0.40 mm |
| ≥50 | ± 1% | ± 0.75% | ||
| Wall Thickness | <4 | ± 12.5% | ± 10% | |
| ≥4~20 | +15%, -12.5% | ± 10% | ||
| >20 | ± 12.5% | ± 10% | ||
| Cold-drawn (rolled) pipe | Outer Diameter | 6~10 | ± 0.20 mm | ± 0.10 mm |
| >10~30 | ± 0.40 mm | ± 0.20 mm | ||
| >30~50 | ± 0.45 mm | ± 0.25 mm | ||
| >50 | ± 1% | ± 0.5% | ||
| Wall Thickness | ≤1 | ± 0.15 mm | ± 0.12 mm | |
| >1~3 | +15%, -10% | ± 10% | ||
| >3 | +12.5%, -10% | ± 10% |
Note: For hot-expanded pipes with an outer diameter of not less than 351 mm, the allowable deviation is ± 18%.
