I. What is Round Seamless Pipe?
Round Seamless Pipe (SCT) is a hollow cylindrical steel made by hot rolling or cold drawing process with perfectly concentric cross sections and no welds.
As the most efficient fluid transport solution in the industrial sector, this type of tube dominates the three main areas of oil and gas pipelines (62% share), machinery manufacturing (21%) and building structures (17%).
According to GB/T 17395-2008 standard, a typical round seamless steel pipe covers an outer diameter of 6-630mm and a wall thickness range of 0.25-50mm. its unique geometric advantages are reflected in:
A. Optimised fluid dynamics: round cross-section reduces flow resistance by up to 30-45
B. Balanced pressure distribution: circumferential stress distribution uniformity is 2-3 times higher than that of profiled pipes
C. Material utilisation: 8-12% savings in steel consumption compared to square tubes
II.Core Advantages and Application Scenarios
1. Excellent engineering performance
The compressive strength of round seamless steel pipe is 15-20% higher than that of welded pipe, especially suitable for:
High-pressure fluid transport (working pressure up to 30MPa)
Precision mechanical drive shafts (tolerance ±0.1mm)
Extreme temperature environment (-40℃ to 450℃)
2.Industry application mapping
| Application | Typical Specifications | Standard | Material Selection |
|---|---|---|---|
| Petroleum and Natural Gas | Φ219×6mm - Φ630×20mm | API SPEC 5CT | J55/K55/N80 steel grades |
| Automotive Manufacturing | Φ25×2.5mm - Φ89×5mm | GB/T 3639 | 20Cr/40Cr alloy steel |
| Boiler Systems | Φ57×3.5mm - Φ159×10mm | GB 5310 | 20G/15CrMoG |
| Hydraulic Equipment | Φ38×1.5mm - Φ108×8mm | GB/T 8713 | ST52/27SiMn |
3. Selection decision matrix
When the following working conditions are encountered, round seamless steel tubes are preferred:
Working pressure > 5MPa
Medium corrosion rate > 0.1mm/year
Temperature fluctuations > 100°C/hour
Rotational stress scenarios
III. In-depth analysis of manufacturing process
1. Hot rolling process (wall thickness ≥ 3mm)
Billet heated to 1200℃ plastic state
Tapered rolls are pierced to form a hollow billet.
Wall thickness tolerance ±7.5% controlled by continuous rolling unit
Online quenching + tempering heat treatment
Advantage: High production efficiency (3-6 metres per minute), suitable for mass production of standard specification round seamless steel tubes.
2. Cold drawing process (wall thickness 0.25-12mm)
Pickling to remove surface oxide layer
Phosphate treatment to enhance lubricity
Multi-pass cold deformation (section shrinkage ≤ 80%)
Bright annealing to eliminate processing stress
Advantage: Dimensional accuracy up to IT9 grade, surface roughness Ra≤0.8μm, suitable for precision hydraulic cylinder barrels and other high-end applications.
IV. International Standards Comparison Table
| Chinese Standard | Corresponding International Standard | Key Parameter Differences |
|---|---|---|
| GB/T 8163 | ASTM A106 | Carbon content upper limit is 0.02% |
| GB 5310 | EN 10216-2 | Impact energy requirement is 15J |
| API 5CT | ISO 11960 | Thread tolerance is stricter by 30% |
V. Seamless steel pipe specification table
| Specification | Specification | Specification |
|---|---|---|
| 12×1.5 | 73×4-4.5-5-6-7-8-9-10-12-15 | 219×30-40 |
| 14×1.5-2.5-3 | 76×4-4.5-5-6-7-8-9-10-12-14 | 245×8-10-14-17-20-22 |
| 16×1.5-2.5-4 | 83×4.5-5-10/12-14-16-18-20 | 245×25-28-30-34-40 |
| 18×2.3-4-5 | 89×4.5-8-10/12-14-16-18-20 | 273×7-9-12-15-18-20-25 |
| 20×2.5-3-5 | 95×4.5-6-8/10-12-14-16-20 | 273×30-35-38-40 |
| 24×2.5-3-4-5-6 | 102×4.5-5-6-7-8-10-12-14-16-20 | 299×8-12-16-20-24-28 |
| 25×2.5-3-4-5-6 | 108×4.5-5-6-7-8-10/12-14-18-20-22 | 299×30-32-36-38-40 |
| 28×3-3.5-4-5-6 | 114×4.5-5-6-7-8-10-12-14-18-20 | 325×8-12-14-18-38 |
| 32×3.5-4-5-6-8 | 121×4.5-5-6-7-8-10-12-14-16-20 | 325×28-32-34-38 |
| 34×4-5-6-8 | 127×4.5-5-6-7-8-10-12-14-16-20 | 351×10-16-20-25-40 |
| 36×3.5-5-6-8 | 133×4.5-6-8-12-14-16-18-20-25-30 | 355×6-18-20-25-30-40 |
| 38×4-5-6-7-8-9-10 | 140×5-6-7-8-9-10/12-14-16-20-22 | 377×8-12-15-20-24-28 |
| 39×3.5-5-8-10 | 146×4.5-6-8-12-14-16-18-20-25-30 | 377×30/37/40 |
| 42×3.5-4-5-6-7-8-9-10 | 152×4.5-6-8-12-14-16-18-20-25-30 | 402×10/15-20-25-30-35 |
| 45×3.5-4-5-6-7-8-9 | 159×4.5-6-10-12-14 | 406×10/20-25-28-35-40 |
| 48×3.5-4-5-6-7-8-9-10 | 159×16-18-20-22-25-30 | 426×10/12-14-16-20-25-30-35-40 |
| 51×3.5-4-5-6-7-8-9-10 | 168×8-10/12/14/20/25/30/35 | 450×10/12-14-16-20-25-34-40 |
| 56×3.5-4-5-6-7-8-9-10 | 180×8-12-16-25-30 | 480×10/12-14-16-18-20-25-30-40 |
| 57×3.5-5-6-7-8-9-10-12 | 180×32-34-38-40 | 500×10/12-14-16-20-25-34-40 |
| 60×3.5-4.5-5-6-7-8-9-12-14 | 194×6-8-12-16-20-25-30-40 | 510×10/12-14-16-20-25-34-40 |
| 63×3.5-4.5-5-6-7-8-9-10-12-14 | 203×6-7-10-15-20-25-30 | 530×10/12-14-16-18-20-30-40 |
| 68×4-4.5-5-6-7-8-9-10-12-14-16 | 203×32-36-40 | - |
| 70×4-4.5-5-6-7-8-9-10-12-15-16 | 219×6-8-12-16-18-20-25 | - |
