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20# Carbon Steel Seamless Pipe: Properties, Sizes and Applications
UN 20# carbon steel seamless pipe is the standard tubing material for boilers, pressure lines, shafts and general machinery. This article explains the 20# grade, its chemical and mechanical properties, standard sizes, and the difference between seamless and welded pipe. All sizes are available as 20# carbon steel seamless pipe from QIDAMT.
What Is 20# Seamless Steel Pipe?
“20#” is a Chinese designation for a high-quality carbon structural steel with a nominal carbon content of about 0.20 %, produced to GB/T 8162 (seamless steel tubes for structural purposes) O GB/T 8163 (seamless steel tubes for liquid service). The pipe is pierced and rolled from a solid billet without any weld seam, which gives it uniform strength around the circumference and makes it suitable for pressure and high-stress service.
Composizione chimica (20#)
| Elemento | C | E | Mn | P | S |
|---|---|---|---|---|---|
| Max (%) | 0.17 – 0.24 | 0.17 – 0.37 | 0.35 – 0.65 | 0.035 | 0.035 |
Proprietà meccaniche
- Yield strength: ≥ 245 MPa
- Tensile strength: ≥ 410 MPa
- Allungamento: ≥ 25 %
- Durezza: ≤ 207 HBW
Standard Sizes (GB/T 8162)
| DI (mm) | Wall (mm) | Weight (kg/m) |
|---|---|---|
| 21.3 | 2.8 – 4.0 | 1.28 – 1.71 |
| 32 | 3.0 – 5.0 | 2.15 – 3.33 |
| 42 | 3.0 – 6.0 | 2.89 – 5.33 |
| 57 | 3.0 – 8.0 | 4.00 – 9.67 |
| 76 | 3.5 – 10.0 | 6.26 – 16.28 |
| 89 | 4.0 – 12.0 | 8.38 – 22.79 |
| 108 – 630 | 4.0 – 40.0 | 10.26 – 582.00 |
Standard lengths: 6 m and 12 m (fixed or random). Superficie: black (mill scale), pickled & oliato, or painted. Ends: plain or beveled for welding.
Seamless vs Welded Pipe
Seamless pipe is formed from a solid billet, so it has no longitudinal weld — it is preferred for pressure, high-temperature and dynamic-loading service. Welded pipe is more economical for large volumes and non-critical lines. For structural frameworks around your piping, QIDAMT also supplies Q235B square tube E Piastra in acciaio Q235B.
Applicazioni
20# seamless pipe is used for boiler tubes, scambiatori di calore, hydraulic cylinders, shafts, supporti strutturali, gas and liquid transmission lines, and general machinery parts. For higher-strength structural steel in the same project, consider Q355B low alloy high strength steel plate.
Buying Checklist
- Specify OD × wall × length and the standard (GB/T 8162 O 8163).
- Confirm surface and end preparation (plain or beveled).
- Ask about hydrostatic test, flattening test and ultrasonic test certificates.
- Request the mill certificate and, for critical service, third-party inspection.
- Bundle small-diameter pipes on steel pallets for safe ocean shipment.
Send OD, wall thickness, length and quantity — we will confirm price, stock and delivery within 24 hours.
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