Brief Introduction to Nominal Pipe Size
Nominal Pipe Size (NPS, frequently used interchangeably with NB (Nominal Bore)) is a U.S.A-developed set of standard sizes for pipes used for high or low pressures and temperatures. According to this standard, a pipe’s size is specified by two non-dimensional numbers: a nominal pipe size (NPS) for diameter based on inches, and a schedule (Sched. or Sch.) for wall thickness. The European designation equivalent to NPS is DN (Nominal Diameter/Diamètre Nominal /Durchmesser Nach Norm), in which pipe sizes are measured in millimeters (mm).
History
Before the year 1927, in the pipeline industry only a small selection of wall thickness were adopted: standard weight (STD), extra-strong (XS) and double extra-strong (XXS) based on the iron pipe size (IPS) system, which did not fit all applications. In March 1927, the American Standards Association authorized a committee to standardize the dimensions of wrought steel, wrought iron pipe and tubing. After a period of survey for the industry, the committee added a system of schedule numbers designating wall thickness to the existing IPS system (renamed afterwards as NPS and the IPS and NPS numbers remaining equivalent.) Since the original schedules were created, there have been many revisions and additions to the tables of pipe sizes based on industry use and on standards fromAPI, ASTM and others.
Due to the common use of stainless steel pipes in the mid 20th century, which permit the use of thinner pipe walls with much less risk of failure due to corrosion, by 1949 thinner schedules 5S and 10S were created, and other "S" sizes followed later.
NPS tables for selected sizes
NPS 1/8 to NPS 3 1/2
NPS |
DN |
OD |
Wall Thickness |
|||||||
|
SCH 5 |
SCH 10s/10 |
SCH 30 |
SCH 40s/40 |
SCH 80s/80 |
SCH 120 |
SCH 160 |
XXS |
|||
|
1/8 |
6 |
0.405 (10.29) |
0.035 (0.889) |
0.049 (1.245) |
0.057 (1.448) |
0.068 (1.727) |
0.095 (2.413) |
-- |
-- |
-- |
|
1/4 |
8 |
0.540 (13.72) |
0.049 (1.245) |
0.065 (1.651) |
0.073 (1.854) |
0.088 (2.235) |
0.119 (3.023) |
-- |
-- |
-- |
|
3/8 |
10 |
0.675 (17.15) |
0.049 (1.245) |
0.065 (1.651) |
0.073 (1.854) |
0.091 (2.311) |
0.126 (3.200) |
-- |
-- |
-- |
|
1/2 |
15 |
0.840 (21.34) |
0.065 (1.651) |
0.083 (2.108) |
0.095 (2.413) |
0.109 (2.769) |
0.147 (3.734) |
-- |
0.188 (4.775) |
0.294 (7.468) |
|
3/4 |
20 |
1.050 (26.67) |
0.065 (1.651) |
0.083 (2.108) |
0.095 (2.413) |
0.113 (2.870) |
0.154 (3.912) |
-- |
0.219 (5.563) |
0.308 (7.823) |
|
1 |
25 |
1.315 (33.40) |
0.065 (1.651) |
0.109 (2.769) |
0.114 (2.896) |
0.133 (3.378) |
0.179 (4.547) |
-- |
0.250 (6.350) |
0.358 (9.093) |
|
1 1/4 |
32 |
1.660 (42.16) |
0.065 (1.651) |
0.109 (2.769) |
0.117 (2.972) |
0.140 (3.556) |
0.191 (4.851) |
-- |
0.250 (6.350) |
0.382 (9.703) |
|
1 1/2 |
40 |
1.900 (48.26) |
0.065 (1.651) |
0.109 (2.769) |
0.125 (3.175) |
0.145 (3.683) |
0.200 (5.080) |
-- |
0.281 (7.137) |
0.400 (10.160) |
|
2 |
50 |
2.375 (60.33) |
0.065 (1.651) |
0.109 (2.769) |
0.125 (3.175) |
0.154 (3.912) |
0.218 (5.537) |
0.250 (6.350) |
0.343 (8.712) |
0.436 (11.074) |
|
2 1/2 |
65 |
2.875 (73.03) |
0.083 (2.108) |
0.120 (3.048) |
0.188 (4.775) |
0.203 (5.156) |
0.276 (7.010) |
0.300 (7.620) |
0.375 (9.525) |
0.552 (14.021) |
|
3 |
80 |
3.500 (88.90) |
0.083 (2.108) |
0.120 (3.048) |
0.188 (4.775) |
0.216 (5.486) |
0.300 (7.620) |
0.350 (8.890) |
0.438 (11.125) |
0.600 (15.240) |
|
3 1/2 |
90 |
4.000 (101.60) |
0.083 (2.108) |
0.120 (3.048) |
0.188 (4.775) |
0.226 (5.740) |
0.318 (8.077) |
-- |
-- |
0.636 (16.154) |
NPS 4 to NPS 9
|
NPS |
DN |
OD |
Wall Thickness |
|||||||
|
SCH 5 |
SCH 10s/10 |
SCH 20 |
SCH 30 |
SCH 40s/40 |
SCH 60 |
SCH 80s/80 |
SCH 100 |
|||
|
4 |
100 |
4.500 (114.30) |
0.083 (2.108) |
0.120 (3.048) |
-- |
0.188 (4.775) |
0.237 (6.020) |
0.281 (7.137) |
0.337 (8.560) |
0.437 (11.100) |
|
4 1/2 |
115 |
5.000 (127.00) |
-- |
-- |
-- |
-- |
0.247 (6.274) |
-- |
0.355 (9.017) |
-- |
|
5 |
125 |
5.563 (141.30) |
0.109 (2.769) |
0.134 (3.404) |
-- |
-- |
0.258 (6.553) |
-- |
0.375 (9.525) |
-- |
|
6 |
150 |
6.625 (168.28) |
0.109 (2.769) |
0.134 (3.404) |
-- |
-- |
0.280 (7.112) |
-- |
0.432 (10.973) |
-- |
|
7 |
-- |
7.625 (193.68) |
-- |
-- |
-- |
-- |
0.301 (7.645) |
-- |
0.500 (12.700) |
-- |
|
8 |
200 |
8.625 (219.08) |
0.109 (2.769) |
0.148 (3.759) |
0.250 (6.350) |
0.277 (7.036) |
0.322 (8.179) |
0.406 (10.312) |
0.500 (12.700) |
0.593 (15.062) |
|
9 |
-- |
9.625 (244.48) |
-- |
-- |
-- |
-- |
0.342 (8.687) |
-- |
0.500 (12.700) |
-- |
NPS 4 to NPS 9
|
NPS |
Wall Thickness |
|||
|
SCH 120 |
SCH 140 |
SCH 160 |
XXS |
|
|
4 |
-- |
-- |
0.531 (13.487) |
0.674 (17.120) |
|
4 1/2 |
-- |
-- |
-- |
0.710 (18.034) |
|
5 |
0.500 (12.700) |
-- |
0.625 (15.875) |
0.750 (19.050) |
|
6 |
0.562 (14.275) |
-- |
0.719 (18.263) |
0.864 (21.946) |
|
7 |
-- |
-- |
-- |
0.875 (22.225) |
|
8 |
0.719 (18.263) |
0.812 (20.625) |
0.906 (23.012) |
0.875 (22.225) |
|
9 |
-- |
-- |
-- |
-- |
NPS 10 to NPS 24
|
NPS |
DN |
OD |
Wall Thickness |
||||||
|
SCH 5s |
SCH 5 |
SCH 10s |
SCH 10 |
SCH 20 |
SCH 30 |
SCH 40s/STD |
|||
|
10 |
250 |
10.75 (273.05) |
0.134 (3.404) |
0.134 (3.404) |
0.165 (4.191) |
0.165 (4.191) |
0.250 (6.350) |
0.307 (7.798) |
0.365 (9.271) |
|
12 |
300 |
12.75 (323.85) |
0.156 (3.962) |
0.165 (4.191) |
0.180 (4.572) |
0.180 (4.572) |
0.250 (6.350) |
0.330 (8.382) |
0.375 (9.525) |
|
14 |
350 |
14.00 (355.60) |
0.156 (3.962) |
0.156 (3.962) |
0.188 (4.775) |
0.250 (6.350) |
0.312 (7.925) |
0.375 (9.525) |
0.375 (9.525) |
|
16 |
400 |
16.00 (406.40) |
0.165 (4.191) |
0.165 (4.191) |
0.188 (4.775) |
0.250 (6.350) |
0.312 (7.925) |
0.375 (9.525) |
0.375 (9.525) |
|
18 |
450 |
18.00 (457.20) |
0.165 (4.191) |
0.165 (4.191) |
0.188 (4.775) |
0.250 (6.350) |
0.312 (7.925) |
0.437 (11.100) |
0.375 (9.525) |
|
20 |
500 |
20.00 (508.00) |
0.188 (4.775) |
0.188 (4.775) |
0.218 (5.537) |
0.250 (6.350) |
0.375 (9.525) |
0.500 (12.700) |
0.375 (9.525) |
|
22 |
550 |
22.00 (558.80) |
0.188 (4.775) |
0.188 (4.775) |
0.218 (5.537) |
0.250 (6.350) |
0.375 (9.525) |
0.500 (12.700) |
0.375 (9.525) |
|
24 |
600 |
24.00 (609.60) |
0.218 (5.537) |
0.218 (5.537) |
0.250 (6.350) |
0.250 (6.350) |
0.375 (9.525) |
0.562 (14.275) |
0.375 (9.525) |
|
NPS |
Wall Thickness |
|||||||
|
SCH 40 |
SCH 60 |
SCH 80s/XS |
SCH 80 |
SCH 100 |
SCH 120 |
SCH 140 |
SCH 160 |
|
|
10 |
0.365 (9.271) |
0.500 (12.700) |
0.500 (12.700) |
0.593 (15.062) |
0.718 (18.237) |
0.843 (21.412) |
1.000 (25.400) |
1.125 (28.575) |
|
12 |
0.406 (10.312) |
0.562 (14.275) |
0.500 (12.700) |
0.687 (17.450) |
0.843 (21.412) |
1.000 (25.400) |
1.125 (28.575) |
1.312 (33.325) |
|
14 |
0.437 (11.100) |
0.593 (15.062) |
0.500 (12.700) |
0.750 (19.050) |
0.937 (23.800) |
1.093 (27.762) |
1.250 (31.750) |
1.406 (35.712) |
|
16 |
0.500 (12.700) |
0.656 (16.662) |
0.500 (12.700) |
0.843 (21.412) |
1.031 (26.187) |
1.218 (30.937) |
1.437 (36.500) |
1.593 (40.462) |
|
18 |
0.562 (14.275) |
0.750 (19.050) |
0.500 (12.700) |
0.937 (23.800) |
1.156 (29.362) |
1.375 (34.925) |
1.562 (39.675) |
1.781 (45.237) |
|
20 |
0.593 (15.062) |
0.812 (20.625) |
0.500 (12.700) |
1.031 (26.187) |
1.280 (32.512) |
1.500 (38.100) |
1.750 (44.450) |
1.968 (49.987) |
|
22 |
-- |
0.875 (22.225) |
0.500 (12.700) |
1.125 (28.575) |
1.375 (34.925) |
1.625 (41.275) |
1.875 (47.625) |
2.125 (53.975) |
|
24 |
0.687 (17.450) |
0.968 (24.587) |
0.500 (12.700) |
1.218 (30.937) |
1.531 (38.887) |
1.812 (46.025) |
2.062 (52.375) |
2.343 (59.512) |
NPS 26 to NPS 36
|
NPS |
DN |
OD |
Wall Thickness |
|||
|
SCH 5s |
SCH 10s |
SCH 10 |
SCH 20 |
|||
|
26 |
650 |
26.000 (660.400) |
-- |
-- |
0.312 (7.925) |
0.500 (12.700) |
|
28 |
700 |
28.000 (711.200) |
-- |
-- |
0.312 (7.925) |
0.500 (12.700) |
|
30 |
750 |
30.000 (762.000) |
0.250 (6.350) |
0.312 (7.925) |
0.312 (7.925) |
0.500 (12.700) |
|
32 |
800 |
32.000 (812.800) |
-- |
-- |
0.312 (7.925) |
0.500 (12.700) |
|
34 |
850 |
34.000 (863.600) |
-- |
-- |
0.312 (7.925) |
0.500 (12.700) |
|
36 |
900 |
36.000 (914.400) |
-- |
-- |
0.312 (7.925) |
0.500 (12.700) |
NPS 26 to NPS 36
|
NPS |
Wall Thickness |
|||
|
SCH 30 |
SCH 40s/STD |
SCH 40 |
SCH 80s/XS |
|
|
26 |
-- |
0.375 (9.525) |
-- |
0.500 (12.700) |
|
28 |
0.625 (15.875) |
0.375 (9.525) |
-- |
0.500 (12.700) |
|
30 |
0.625 (15.875) |
0.375 (9.525) |
-- |
0.500 (12.700) |
|
32 |
0.625 (15.875) |
0.375 (9.525) |
0.688 (17.475) |
0.500 (12.700) |
|
34 |
0.625 (15.875) |
0.375 (9.525) |
0.688 (17.475) |
0.500 (12.700) |
|
36 |
0.625 (15.875) |
0.375 (9.525) |
0.750 (19.050) |
0.500 (12.700) |
Additional sizes (NPS)
|
NPS |
DN |
OD |
Wall Thickness |
|
|
SCH STD |
SCH XS |
|||
|
40 |
1000 |
40.000 (1,016.000) |
0.375 (9.525) |
0.500 (12.700) |
|
42 |
1050 |
42.000 (1,066.800) |
0.375 (9.525) |
0.500 (12.700) |
|
44 |
1100 |
44.000 (1,117.600) |
0.375 (9.525) |
0.500 (12.700) |
|
46 |
1150 |
46.000 (1,168.400) |
0.375 (9.525) |
0.500 (12.700) |
|
48 |
1200 |
48.000 (1,219.200) |
0.375 (9.525) |
0.500 (12.700) |
|
52 |
1300 |
52.000 (1,320.800) |
-- |
-- |
|
56 |
1400 |
56.000 (1,422.400) |
-- |
-- |
|
60 |
1500 |
60.000 (1,524.000) |
-- |
-- |
|
64 |
1600 |
64.000 (1,625.600) |
-- |
-- |
|
68 |
1700 |
68.000 (1,727.200) |
-- |
-- |
|
72 |
1800 |
72.000 (1,828.800) |
-- |
-- |
|
76 |
1900 |
76.000 (1,930.400) |
-- |
-- |
|
80 |
2000 |
80.000 (2,032.000) |
-- |
-- |
|
88 |
2200 |
88.000 (2,235.200) |
-- |
-- |
Table Instructions
Based on the NPS and a pipe schedule, the pipe outside diameter (OD) and wall thickness can be obtained from reference tables defined as below, which are based on ASME standards B36.10M and B36.19M.
- For NPS 1/8 to 12 inches, the NPS and OD values are different. (These NPS values were originally set to give the same inside diameter (ID) based on wall thicknesses standard at the beginning.) For example, the OD of an NPS 12 pipe is actually 12.75 inches. To find the actual OD for each NPS value, refer to the tables below. (Note that for tubing, the size is always the actual OD.)
- For NPS 14 inches and up, the NPS and OD values are equal. For example, NPS 14 Sch. 40 has an OD of 14 inches and a wall thickness of 0.437 inches.
For a given NPS, the OD stays fixed and the wall thickness increases with schedule. For a given schedule, the OD increases with NPS while the wall thickness stays constant or increases. Using equations and rules in ASME B31.3 Process Piping, it can be shown that pressure rating decreases with increasing NPS and constant schedule.
Some specifications use STD, XS and XXS in the older IPS system. STD is identical to SCH 40S, and 40S is identical to 40 for NPS 1/8 to NPS 10, inclusive. XS is identical to SCH 80S, and 80S is identical to 80 for NPS 1/8 to NPS 8, inclusive. XXS wall is thicker than schedule 160 from NPS 1/8" to NPS 6" inclusive, and schedule 160 is thicker than XXS wall for NPS 8" and larger.
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