NPS 18 (DN 450) Pipe — Dimensions, Schedules & Weight
Welded and seamless steel pipe per ASME B36.10M / EN 10220
NPS 18 (DN 450) pipe always has an outside diameter of 457 mm (17.992") — the schedule changes only the wall, from 6.35 mm at Sch 10 to 45.24 mm at Sch 160. That is the whole logic of the schedule system: OD stays constant so fittings and threads always match, while a higher schedule buys pressure capacity with a thicker wall and a smaller bore.
The most-quoted variant, Sch STD, has a 9.53 mm wall, a 437.9 mm inside diameter, and weighs 105.16 kg/m — a 6 m length is 631 kg. All weights below are plain-end masses from the standard formula (OD − t) × t × 0.02466.
NPS 18 (DN 450) pipe, Sch STD: cross-section drawn to scale (OD 457 mm, wall 9.53 mm, ID 437.9 mm)NPS 18 (DN 450) — all schedules
| Schedule | t (mm) | t (in) | ID (mm) | kg/m | lb/ft |
|---|
| Sch 10 | 6.35 | 0.25 | 444.3 | 70.57 | 47.42 |
| Sch 20 | 7.92 | 0.312 | 441.2 | 87.71 | 58.94 |
| Sch STD | 9.53 | 0.375 | 437.9 | 105.16 | 70.66 |
| Sch 30 | 11.13 | 0.438 | 434.7 | 122.38 | 82.23 |
| Sch XS | 12.7 | 0.5 | 431.6 | 139.15 | 93.5 |
| Sch 40 | 14.27 | 0.562 | 428.5 | 155.8 | 104.69 |
| Sch 60 | 19.05 | 0.75 | 418.9 | 205.74 | 138.25 |
| Sch 80 | 23.83 | 0.938 | 409.3 | 254.55 | 171.05 |
| Sch 100 | 29.36 | 1.156 | 398.3 | 309.62 | 208.05 |
| Sch 120 | 34.93 | 1.375 | 387.1 | 363.56 | 244.3 |
| Sch 140 | 39.67 | 1.562 | 377.7 | 408.26 | 274.34 |
| Sch 160 | 45.24 | 1.781 | 366.5 | 459.37 | 308.68 |
Frequently Asked Questions
What is the outside diameter of 18" pipe?
457 mm (17.992 inches) — for every schedule. NPS is a nominal name, not a measurement. From NPS 14 up, OD equals the NPS in inches.
What is the wall thickness and ID of 18" Sch STD?
Sch STD has a 9.53 mm (0.375") wall, which leaves an inside diameter of 437.9 mm. The table above lists the wall and bore for every schedule of this size.
How much does 18" Sch STD pipe weigh?
105.16 kg/m (70.66 lb/ft). A 6 m length weighs 631 kg, a 12 m length 1,261.9 kg. The heaviest listed schedule, Sch 160, weighs 459.37 kg/m.
What is the difference between STD and Schedule 40?
Up to NPS 10 they are the same wall. From NPS 12 upward they split: STD stays at 9.53 mm (3/8") for all larger sizes, while Sch 40 keeps growing with the diameter. The same happens to XS and Sch 80 above NPS 8.
Values are entered from the governing standard’s published tables and cross-checked programmatically against its mass and section formulas before publication. Spotted an error? Write to advertising@metalabout.net — verified corrections ship within days. About