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Nominal Pipe Size
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1 History 2 Application 3 NPS tables for selected sizes o 3.1 NPS ⅛ to NPS 3½ o 3.2 NPS 4 to NPS 9 o 3.3 NPS 10 to NPS 24 4 See also 5 Sources 6 References

Nominal Pipe Size (NPS) is a North American set of standard sizes for pipes used for high or low pressures and temperatures.[1] Pipe size is specified with two non-dimensional numbers: a nominal pipe size (NPS) based on inches, and a schedule (Sched. or Sch.). NPS is often incorrectly called National Pipe Size, due to confusion with national pipe thread (NPT). For other pipe size standards, see pipe (material) - sizes. The European designation equivalent to NPS is DN (diamètre nominal/nominal diameter), in which sizes are measured in millimetres.[2] The term NB (nominal bore) is also frequently used interchangeably with NPS.

[edit] History
In March 1927, the American Standards Association authorized a committee to standardize the dimensions of wrought steel and wrought iron pipe and tubing. At that time only a small selection of wall thicknesses were in use: standard weight (STD), extra-strong

(XS), and double extra-strong (XXS), based on the iron pipe size (IPS) system of the day. However these three sizes did not fit all applications. The committee surveyed the industry and created a system of schedule numbers that designated wall thicknesses based on smaller steps between sizes,[3] although IPS and NPS numbers remain equivalent. The original intent was that each schedule would relate to a given pressure rating, however the numbers deviated so far from wall thicknesses in common use that this original intent could not be accomplished.[3][4] Also, in 1939, it was hoped that the designations of STD, XS, and XXS would be phased out by schedule numbers, however those original terms are still in common use today (although sometimes referred to as standard, extra-heavy (XH), and double extra-heavy (XXH), respectively). 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 from API, ASTM, and others.[3] Stainless steel pipes, which were coming into more common use in the mid 20th century, permitted the use of thinner pipe walls with much less risk of failure due to corrosion. By 1949 thinner schedules 5S and 10S, which were based on the pressure requirements modified to the nearest BWG number, had been created, and other "S" sizes followed later. Due to their thin walls, the smaller "S" sizes can not be threaded together according to ASME code, but must be fusion welded.[5]

[edit] Application
Based on the NPS and schedule of a pipe, the pipe outside diameter (OD) and wall thickness can be obtained from reference tables such as those below, which are based on ASME standards B36.10M and B36.19M. For example, NPS 14 Sch 40 has an OD of 14 inches and a wall thickness of 0.437 inches. However the NPS and OD values are not always equal, which can create confusion.




For NPS ⅛ to 12 inches, the NPS and OD values are different. 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. In other words, an NPS 14 pipe is actually 14 inches OD.

The reason for the discrepancy for NPS ⅛ to 12 inches is that these NPS values were originally set to give the same inside diameter (ID) based on wall thicknesses standard at the time. However, as the set of available wall thicknesses evolved, the ID changed and NPS became only indirectly related to ID and OD.

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.[4] Some specifications use pipe schedules called standard wall (STD), extra strong (XS), and double extra strong (XXS), although these actually belong to an older system called iron pipe size (IPS). The IPS number is the same as the NPS number. 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. Different definitions exist for XXS, but it is generally thicker than schedule 160. The "S" designation, for example "NPS Sch 10S", most often indicates stainless steel pipes. However some stainless steel pipes are available in steel designations, so strictly speaking the "S" designation only differentiates B36.19M pipe from B36.10M pipe.[1] Both polyvinyl chloride pipe (PVC) and chlorinated polyvinyl chloride pipe (CPVC) are made in NPS sizes.

[edit] NPS tables for selected sizes
[edit] NPS ⅛ to NPS 3½
[6]

NPS ⅛ ¼ ⅜ ½ ¾

DN mm 6 8 10 15

OD inches (millimeters) 0.405 in (10.29 mm) 0.540 in (13.72 mm) 0.675 in (17.15 mm) 0.840 in (21.34 mm)

Wall Thickness inches (millimeters) SCH 5 0.035 in (0.889 mm) 0.049 in (1.245 mm) 0.049 in (1.245 mm) 0.065 in (1.651 mm) 0.065 in SCH 10 0.049 in (1.245 mm) 0.065 in (1.651 mm) 0.065 in (1.651 mm) 0.083 in (2.108 mm) 0.083 in SCH 30 0.057 in (1.448 mm) 0.073 in (1.854 mm) 0.073 in (1.854 mm) 0.095 in (2.413 mm) 0.095 in SCH 40 0.068 in (1.727 mm) 0.088 in (2.235 mm) 0.091 in (2.311 mm) 0.109 in (2.769 mm) 0.113 in SCH 80 0.095 in (2.413 mm) 0.119 in (3.023 mm) 0.126 in (3.200 mm) 0.147 in (3.734 mm) 0.154 in SCH 120 ------0.170 in (4.318 mm) --------0.294 in (7.468 mm) 0.308 in XXS

20 1.050 in

(26.67 mm) 1 1¼ 1½ 2 2½ 3 3½ 25 32 40 50 65 80 90 1.315 in (33.40 mm) 1.660 in (42.16 mm) 1.900 in (48.26 mm) 2.375 in (60.33 mm) 2.875 in (73.02 mm) 3.500 in (88.90 mm) 4.000 in (101.60 mm)

(1.651 mm) 0.065 in (1.651 mm) 0.065 in (1.651 mm) 0.065 in (1.651 mm) 0.065 in (1.651 mm) 0.083 in (2.108 mm) 0.083 in (2.108 mm) 0.083 in (2.108 mm)

(2.108 mm) 0.109 in (2.769 mm) 0.109 in (2.769 mm) 0.109 in (2.769 mm) 0.109 in (2.769 mm) 0.120 in (3.048 mm) 0.120 in (3.048 mm) 0.120 in (3.048 mm)

(2.413 mm) 0.114 in (2.896 mm) 0.117 in (2.972 mm) 0.125 in (3.175 mm) 0.125 in (3.175 mm) 0.188 in (4.775 mm) 0.188 in (4.775 mm) 0.188 in (4.775 mm)

(2.870 mm) 0.133 in (3.378 mm) 0.140 in (3.556 mm) 0.145 in (3.683 mm) 0.154 in (3.912 mm) 0.203 in (5.156 mm) 0.216 in (5.486 mm) 0.226 in (5.740 mm)

(3.912 mm) 0.179 in (4.547 mm) 0.191 in (4.851 mm) 0.200 in (5.080 mm) 0.218 in (5.537 mm) 0.276 in (7.010 mm) 0.300 in (7.620 mm) 0.318 in (8.077 mm) ------0.250 in (6.350 mm) 0.300 in (7.620 mm) 0.350 in (8.890 mm) ---

(7.823 mm) 0.358 in (9.093 mm) 0.382 in (9.703 mm) 0.400 in (10.160 mm) 0.436 in (11.074 mm) 0.552 in (14.021 mm) 0.600 in (15.240 mm) 0.636 in (16.154 mm)

[edit] NPS 4 to NPS 9
Wall Thickness OD inches (millimeters) NPS DN inches [6] mm (millim SCH eters) SCH 5 SCH 10 SCH 20 SCH 30 40/STD SCH 60 SCH 80 SCH 100 SCH 120 SCH 140 SCH 160 4 4.500 0.083 in 0.120 in in (2.108 (3.048 --100 (114.30 mm) mm) mm) 5.000 --115 in (127.00 ----0.188 in 0.237 in 0.281 in 0.337 in (4.775 (6.020 (7.137 m (8.560 m --mm) mm) m) m) --0.247 in (6.274 --mm) 0.355 in (9.017 m --m) 0.437 in (11.100 mm) ----0.531 in (13.487 mm) ---



---

mm) 5 5.563 0.109 in 0.134 in in (2.769 (3.404 --125 (141.30 mm) mm) mm) 6.625 0.109 in 0.134 in in (2.769 (3.404 --150 (168.27 mm) mm) mm) --0.258 in (6.553 --mm) 0.280 in (7.112 --mm) 0.375 in (9.525 m --m) 0.432 in (10.973 mm) 0.500 in (12.700 mm) 0.500 in (12.700 mm) 0.562 in (14.275 mm) 0.718 in (18.237 mm) --0.625 in (15.875 mm) 0.719 in (18.263 mm) 0.906 in (23.012 mm)

6

---

---

---

8

8.625 0.109 in 0.148 in 0.250 in 0.277 in 0.322 in 0.406 in in (2.769 (3.759 (6.350 (7.036 (8.179 (10.312 200 (219.08 mm) mm) mm) mm) mm) mm) mm)

0.593 in (15.062 mm)

0.812 in (20.625 mm)

[edit] NPS 10 to NPS 24
[6]

NPS

DN mm 250 300 350 400 450

OD inches (millimeters) 10.75 in (273.05 mm) 12.75 in (323.85 mm) 14.00 in (355.60 mm) 16.00 in (406.40 mm) 18.00 in (457.20 mm)

Wall Thickness inches (millimeters) SCH 5s 0.134 in (3.404 mm) 0.156 in (3.962 mm) 0.156 in (3.962 mm) 0.165 in (4.191 mm) 0.165 in (4.191 mm) SCH 5 0.134 in (3.404 mm) 0.165 in (4.191 mm) 0.156 in (3.962 mm) 0.165 in (4.191 mm) 0.165 in (4.191 mm) SCH 10s 0.165 in (4.191 mm) 0.180 in (4.572 mm) 0.188 in (4.775 mm) 0.188 in (4.775 mm) 0.188 in (4.775 mm) SCH 10 0.165 in (4.191 mm) 0.180 in (4.572 mm) 0.250 in (6.350 mm) 0.250 in (6.350 mm) 0.250 in (6.350 mm) SCH 20 0.250 in (6.350 mm) 0.250 in (6.350 mm) 0.312 in (7.925 mm) 0.312 in (7.925 mm) 0.312 in (7.925 mm) SCH 30 0.307 in (7.798 mm) 0.330 in (8.382 mm) 0.375 in (9.525 mm) 0.375 in (9.525 mm) 0.437 in (11.100 mm)

10 12 14 16 18

20 24

500 600

20.0 in (508.00 mm) 24.00 in (609.60 mm)

0.188 in (4.775 mm) 0.218 in (5.537 mm)

0.188 in (4.775 mm) 0.218 in (5.537 mm)

0.218 in (5.537 mm) 0.250 in (6.350 mm)

0.250 in (6.350 mm) 0.250 in (6.350 mm)

0.375 in (9.525 mm) 0.375 in (9.525 mm)

0.500 in (12.700 mm) 0.562 in (14.275 mm)

NPS

[6]

Wall Thickness inches (millimeters) SCH 40s SCH 40 0.365 in 0.365 in (9.271 mm) (9.271 mm) SCH 60 SCH 80s SCH 80 SCH 100 SCH 120 SCH 140 SCH 160 0.500 in 0.500 in 0.593 in 0.718 in 0.843 in 1.000 in 1.125 in (12.700 mm) (12.700 mm) (15.062 mm) (18.237 mm) (21.412 mm) (25.400 mm) (28.575 mm)

10 12 14 16 18 20 24

0.375 in 0.406 in 0.500 in 0.500 in 0.687 in 0.843 in 1.000 in 1.125 in 1.312 in (9.525 mm) (10.312 mm) (12.700 mm) (12.700 mm) (17.450 mm) (21.412 mm) (25.400 mm) (28.575 mm) (33.325 mm) 0.375 in 0.437 in 0.593 in 0.500 in 0.750 in 0.937 in 1.093 in 1.250 in 1.406 in (9.525 mm) (11.100 mm) (15.062 mm) (12.700 mm) (19.050 mm) (23.800 mm) (27.762 mm) (31.750 mm) (35.712 mm) 0.375 in 0.500 in 0.656 in 0.500 in 0.843 in 1.031 in 1.218 in 1.437 in 1.593 in (9.525 mm) (12.700 mm) (16.662 mm) (12.700 mm) (21.412 mm) (26.187 mm) (30.937 mm) (36.500 mm) (40.462 mm) 0.375 in 0.562 in 0.750 in 0.500 in 0.937 in 1.156 in 1.375 in 1.562 in 1.781 in (9.525 mm) (14.275 mm) (19.050 mm) (12.700 mm) (23.800 mm) (29.362 mm) (34.925 mm) (39.675 mm) (45.237 mm) 0.375 in 0.593 in 0.812 in 0.500 in 1.031 in 1.280 in 1.500 in 1.750 in 1.968 in (9.525 mm) (15.062 mm) (20.625 mm) (12.700 mm) (26.187 mm) (32.512 mm) (38.100 mm) (44.450 mm) (49.987 mm) 0.375 in 0.687 in 0.968 in 0.500 in 1.218 in 1.531 in 1.812 in 2.062 in 2.343 in (9.525 mm) (17.450 mm) (24.587 mm) (12.700 mm) (30.937 mm) (38.887 mm) (46.025 mm) (52.375 mm) (59.512 mm)

Note: --- = size not designated.

[edit] See also

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British standard pipe sizes British standard pipe thread sizes Pipe sizes

[edit] Sources


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Oberg, Erik; Franklin D. Jones, Holbrook L. Horton, and Henry H. Ryffel (2000). ed. Christopher J. McCauley, Riccardo Heald, and Muhammed Iqbal Hussain. ed. Machinery's Handbook (26th Edition ed.). New York: Industrial Press Inc.. ISBN 0-8311-2635-3. Nayyar, P.E., Mohinder L. (2000). "A1". in Mohinder L. Nayyar, P.E.. Piping Handbook (7th ed.). New York: McGraw-Hill. ISBN 0-07-047106-1. Engineering Department (1988). Flow of Fluids Through Valves, Fittings, and Pipe (Technical Paper No. 410) (25th Printing—1991 ed.). Joliet, IL: Crane Co.. ASME B36.10M - Welded and Seamless Wrought Steel Pipe. ANSI/ASME Standard 36.19M - Stainless Steel Pipe. ANSI/ASTM Reference R0036 - Stainless Steel Pipe.

[edit] References
^ a b ASME B36.10M-2004, p. 1 ^ NPS - "Nominal Pipe Size" and DN - "Diamètre Nominale", EngineeringToolbox.com ^ a b c ASME B36.10M-2004, p. iv ^ a b This is contrary to the McGraw Hill Piping Handbook, which says that the schedule number can be converted to pressure by dividing the schedule by 1000 and multiplying by the allowable stress of the material. [Nayyar and Mohinder, 2000.] 5. ^ ASME Standard 36.19M-2004, p. iv 6. ^ a b c d Table of Pipe Schedules from EngineersEdge.com. Table shows additional schedules, sizes and sizes greater than 24". 1. 2. 3. 4. Retrieved from "http://en.wikipedia.org/wiki/Nominal_Pipe_Size" Categories: Piping | Mechanical standards
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