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Carbon Steel Pipe Schedule: Sch 40 vs Sch 80 Πάχος Τοίχου
Carbon Steel Pipe Schedule: Sch 40 vs Sch 80 Πάχος Τοίχου
Steel pipe “πρόγραμμα” (Sch 40, Sch 80, Sch 160) defines the wall thickness for a given nominal diameter, and it is one of the most frequently mis-specified parameters in piping. This guide explains what the numbers mean, how Sch 40 compares to Sch 80, and how to choose the right schedule for pressure service.
What Schedule Means
Schedule is a dimensionless number that determines wall thickness. For a given nominal pipe size (NPS), higher schedule means thicker wall and smaller inside diameter. Sch 40 is the standard wall for general plumbing, HVAC and low-pressure process piping. Sch 80 has roughly twice the wall thickness, used for higher pressure or corrosive service. Sch 160 is the extra-heavy wall for very high pressure. The outside diameter stays the same across schedules — only the inside diameter changes. Δείτε το δικό μας Q345D seamless pipe.
| NPS | Sch 40 τείχος (mm) | Sch 80 τείχος (mm) | Sch 160 τείχος (mm) |
|---|---|---|---|
| 1/2″ | 3.91 | 5.54 | 7.47 |
| 1″ | 4.55 | 6.35 | 8.38 |
| 2″ | 5.54 | 7.62 | 11.07 |
| 4″ | 6.02 | 9.53 | 13.49 |
| 6″ | 7.11 | 10.97 | 14.27 |
Why Wall Thickness Matters
Thicker wall handles higher internal pressure. For a given material, pressure rating scales with wall thickness divided by outside diameter. Sch 80 pipe handles roughly 1.5× the pressure of Sch 40 at the same size. The trade-off is that thicker wall reduces inside diameter, which reduces flow capacity — a 2″ Sch 80 pipe has about 15 % less internal flow area than a 2″ Sch 40. For gravity flow or low-pressure water, Sch 40 is sufficient; for steam, high-pressure oil or gas, Sch 80 or higher is required by code.
Buying Advice
Never specify “1 σωλήνα ίντσας” without the schedule — suppliers default to Sch 40, which may not meet your pressure rating. For structural pipe (κιγκλιδώματα, στύλους φράχτη), Sch 40 or even STD is fine because pressure is not a concern. For process piping, always run the pressure calculation per ASME B31.3 and specify the schedule accordingly. Also note that “σωλήνας” και “σωλήνας” are different: pipe is specified by nominal diameter and schedule, while tube is specified by exact outside diameter and wall thickness.
