Schedule is a wall-thickness class, not a size. For any given NPS the outside diameter never changes — SCH 80 pipe is the same OD as SCH 40 but with a thicker wall, a smaller bore and roughly 30–60% more steel per meter. Higher schedule = higher pressure rating at the same grade. Nikasteel supplies SCH 40/80, STD/XS/XXS seamless and welded pipe from 1/2" to 24", MOQ 5 tons, with EN 10204 3.1 MTCs.
Pipe ordering goes wrong in a predictable way: a buyer sends "2 inch pipe" and receives whatever wall the mill had running that week. The fix is understanding three numbers — NPS, OD and schedule — and writing all of them on the PO. This guide covers the ASME B36.10 system used across most international projects.
NPS, OD and Schedule — The Three Numbers
NPS (Nominal Pipe Size) is a name, not a measurement: NPS 2 is neither 2" OD nor 2" bore. OD is fixed by the standard (NPS 2 = 60.3 mm, NPS 4 = 114.3 mm). Schedule selects the wall thickness — and since OD is fixed, a bigger schedule always means a smaller inside diameter:
- SCH 5S/10S — thin wall, mostly stainless lines
- SCH 40 / STD — the default for water, air, structural, fire lines
- SCH 80 / XS — higher pressure, steam, chemical, heavy traffic sleeves
- SCH 160 / XXS — small-bore high-pressure
Dimensions and Weight: 1/2" to 8"
| NPS | OD (mm) | SCH40 wall | SCH40 kg/m | SCH80 wall | SCH80 kg/m |
|---|---|---|---|---|---|
| 1/2" | 21.3 | 2.77 mm | 1.27 | 3.73 mm | 1.62 |
| 3/4" | 26.7 | 2.87 mm | 1.69 | 3.91 mm | 2.20 |
| 1" | 33.4 | 3.38 mm | 2.50 | 4.55 mm | 3.24 |
| 2" | 60.3 | 3.91 mm | 5.44 | 5.54 mm | 8.63 |
| 4" | 114.3 | 6.02 mm | 16.07 | 8.56 mm | 22.32 |
| 6" | 168.3 | 7.11 mm | 28.26 | 10.97 mm | 42.56 |
| 8" | 219.1 | 8.18 mm | 42.55 | 12.70 mm | 64.64 |
Weights are plain-end carbon steel (7.85 kg/dm³). Galvanized pipe adds roughly 3–6% depending on wall.
How Schedule Affects Pressure
Allowable pressure scales roughly with wall thickness for a given grade and temperature. Two examples with A106 Gr B seamless (S = 20,000 psi at ambient):
- NPS 2 SCH 40: ≈ 1,180 psi (81 bar) design pressure at room temperature
- NPS 2 SCH 80: ≈ 1,830 psi (126 bar) — about 55% more, from the same OD pipe
Two cautions: allowable stress drops sharply with temperature (A106 Gr B is derated ~30% by 400 °C), and threaded fittings reduce the working pressure one class. Let the governing code (ASME B31.1 power piping, B31.3 process) make the final call.
Grades That Go With Schedules
| Use | Common specification | Notes |
|---|---|---|
| Pressure piping | ASTM A106 Gr B seamless | High-temp service, hydro tested |
| Structural / columns | ASTM A500 Gr B/C | Also round HSS; check tolerance class |
| General / water | ASTM A53 Gr B (E or S) | Welded or seamless, galvanized option |
| Chinese equivalent | GB/T 8163 20# (seamless) | Fluid service; 45# for higher strength |
How to Write a Pipe Order
- Size in NPS + schedule: "6" NPS × SCH 80" — never just "6 inch pipe".
- Manufacturing method: seamless (SML) or ERW; A106 is seamless only.
- Grade + standard: ASTM A106 Gr B / A53 Gr B / GB 20#.
- Ends: plain end (PE), bevelled for welding (BE), or threaded + coupling (T&C).
- Length: single random (SRL 5–7 m), double random (DRL 10–13 m) or fixed.
- Coating: black, varnished, galvanized, or 3LPE FBE for buried lines.
- Tests: hydro per standard, EN 10204 3.1 MTC, optional PMI for alloy look-alikes.
Cross-check your structural sections with the H-beam size chart, or see our full steel pipe range for sizes beyond this table.
Pipe Quoted to Your Exact Schedule
SCH 40/80, STD/XS/XXS — seamless A106B, ERW A53B, galvanized — 1/2" to 24", MOQ 5 tons, MTC with every heat.
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