Schedule numbers (SCH10, SCH40, SCH80, SCH160…) define pipe and butt weld fitting wall thickness. This guide explains what schedules mean, how they map to STD/XS/XXS designations, and which schedule to choose.
Schedule Quick Reference (Carbon Steel Pipe)
| NPS | OD (in) | SCH10 wall (in) | SCH40/STD wall (in) | SCH80/XS wall (in) |
|---|---|---|---|---|
| 1 | 1.315 | 0.109 | 0.133 | 0.179 |
| 2 | 2.375 | 0.109 | 0.154 | 0.218 |
| 4 | 4.500 | 0.120 | 0.237 | 0.337 |
| 6 | 6.625 | 0.134 | 0.280 | 0.432 |
| 8 | 8.625 | 0.148 | 0.322 | 0.500 |
| 12 | 12.750 | 0.180 | 0.375 | 0.500 |
| 24 | 24.000 | 0.250 | 0.500 | 0.750 |
Schedule vs STD / XS / XXS
The older designations map to schedules differently per size: STD = SCH40 for NPS 10″ and below; XS = SCH80 up to 8″; XXS is heavier than SCH160 in small sizes. Above 10″, STD walls diverge from SCH40 (SCH40 becomes thicker). This is why both systems appear on drawings – always quote the schedule number to be unambiguous.
Which Schedule to Choose
- SCH10/5S – low pressure utility lines, stainless process lines, jacketed services
- SCH40/STD – the process piping default: water, air, steam, most hydrocarbons
- SCH80/XS – higher pressure, corrosive service with corrosion allowance, mechanical strength needs
- SCH160/XXS – high pressure headers, severe service, high-integrity welds
Fittings follow the pipe schedule – a SCH80 elbow has SCH80 walls at the weld end so the joint is full-strength. Corrosion allowance (typically 1.5-3mm) is added to the pressure design: a line needing 4mm for pressure plus 3mm allowance orders SCH80 rather than SCH40. Confirm with your piping spec; we supply all schedules with EN 10204 3.1 certificates. Ask for a schedule review.
FAQs
Does schedule affect fitting dimensions? Only wall thickness and weight – center-to-end dimensions per B16.9 stay the same.
Is SCH40 always STD? For NPS 10″ and below yes; above 10″ they differ – always use the schedule number on POs.
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