ASME B36.19M (stainless steel pipe) · DN 450
Outside diameter 18.000" (457.20 mm), wall 0.375" (9.53 mm), inside diameter 17.250" (438.14 mm).
| Trade size | NPS 18 · DN 450 |
|---|---|
| Schedule | Schedule 40S · also STD |
| Standard | ASME B36.19M (stainless steel pipe) |
| Outside diameter | 18.000" · 457.20 mm · designated 457 mm in the metric column |
| Wall thickness | 0.375" · 9.53 mm |
| Inside diameter | 17.250" · 438.14 mm |
| Weight, plain end | not published |
Nominal Pipe Size is a label, not a measurement. NPS 18 pipe has an outside diameter of 18.000 inches, and it keeps that outside diameter in every schedule made. What the schedule number changes is the wall: at schedule 40s the wall is 0.375 inches, so the bore comes out at 17.250 inches.
That is the practical consequence. Fittings, flanges, supports and threading dies are sized to the outside diameter, so they fit any schedule of the same trade size. Flow, pressure drop and anything that has to pass through the pipe depend on the inside diameter, which changes with every schedule. Order by trade size and schedule; work your hydraulics from the bore.
Same outside diameter of 18.000 inches throughout - only the wall and the bore move.
| Schedule | Wall (in) | ID (in) | Weight (lb/ft) |
|---|---|---|---|
| Schedule 5 | 0.165 | 17.670 | 31.46 |
| Schedule 10 | 0.250 | 17.500 | 47.44 |
| Schedule 20 | 0.312 | 17.376 | 58.94 |
| Schedule 30 | 0.438 | 17.124 | 82.23 |
| Schedule 40 | 0.562 | 16.876 | 104.67 |
| Schedule 60 | 0.750 | 16.500 | 138.3 |
| Schedule 80 | 0.938 | 16.124 | 171.08 |
| Schedule 100 | 1.156 | 15.688 | 208.15 |
| Schedule 120 | 1.375 | 15.250 | 244.37 |
| Schedule 140 | 1.562 | 14.876 | 274.48 |
| Schedule 160 | 1.781 | 14.438 | 308.79 |
| Standard wall (STD) | 0.375 | 17.250 | 70.65 |
| Extra strong (XS) | 0.500 | 17.000 | 93.54 |
| Schedule 5S | 0.165 | 17.670 | not published |
| Schedule 10S | 0.188 | 17.624 | not published |
| Schedule 80S | 0.500 | 17.000 | not published |
0.375 inches (9.53 mm). The outside diameter is 18.000 inches (457.20 mm) whatever the schedule, so this wall leaves an inside diameter of 17.250 inches.
17.250 inches (438.14 mm). Inside diameter is outside diameter minus twice the wall: 18.000 - 2 x 0.375 = 17.250 inches.
No. NPS 18 is a trade size, not a measurement. The pipe measures 18.000 inches across the outside and 17.250 inches across the bore in this schedule. Only the outside diameter is fixed across schedules.
Yes, at NPS 18. STD is the same 0.375 inch wall here. That coincidence is per size and does not hold everywhere: standard wall and schedule 40 part company above NPS 10, and extra strong and schedule 80 part company above NPS 8.
This table runs from NPS 1/8 to NPS 24 and stops there. ASME B36.10M itself continues to NPS 80; those larger sizes are not carried here, so a size above NPS 24 is missing rather than undefined.
Dimensions are as defined by ASME B36.19M (stainless steel pipe). This site is an independent reference and is not affiliated with, endorsed by or approved by any standards body.
Every value on this page was cross-checked against 2 independent published sources:
Nearby sizes