Nominal Pipe Size
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Nominal Pipe Size (NPS) is a set of standard pipe sizes used for pressure piping in North America. The same pipe dimensions are used with different names in Europe. It is often incorrectly called National Pipe Size, due to confusion with National pipe thread. For other pipe size standards, see pipe (material).
Pipe size is specified with two non-dimensional numbers: a Nominal Pipe Size (NPS) and a schedule (SCH). The relationship of these numbers to the actual pipe dimensions is a bit strange. The NPS is very loosely related to the inside diameter in inches, but only for NPS 1/8 to NPS 12. For NPS 14 and larger, the NPS is equal to the outside diameter (OD) in inches. For a given NPS, the OD stays constant and the wall thickness increases with larger SCH. For a given SCH, the OD increases with increasing NPS while the wall thickness increases or stays constant.
For example, a 3/8" Schedule 40 (Standard) pipe has an OD of .675" and a wall thickness of .091". The 3/8" refers to the flow requirement, calculated based on volumetric flow rate need. For an application requiring a certain flow, equivalent to a 3/8" diameter column of fluid (typically water), one would select this pipe. So, the naming convention is more related to the flow than the actual dimensions of the pipe.
Pipe sizes are documented by a number of standards, including API 5L, ANSI/ASME B36.10M in the US, BS 1600 and BS EN 10255 in the United Kingdom and Europe, and ISO 65 internationally. The ISO and European standard uses the same pipe ID's and wall thicknesses, but labels them with a Diametre Nominal (DN) instead of NPS. For NPS of 5 and larger, the DN is equal to the NPS multiplied by 25 (not 25.4).
The most commonly used schedules today are 40, 80, and 160. There is a commonly held belief that the schedule number is an indicator of the service pressure that the pipe can take. For example, the McGraw Hill Piping Handbook says the schedule number can be converted to pressure by dividing the schedule by 1000 and multiplying by the allowable stress of the material (Ref. #2). However, this is not true. Using equations and rules in ASME B31.3 Process Piping, it is easily shown that pressure rating actually goes down with increasing NPS and constant schedule.
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The various standards for pipe schedule are not identical. Frequently some sizes—or even entire schedules—are present in some standards but not others. When different standards do overlap, they usually have the same dimensions. For this reason, the source of the schedules is not distinguished in the table below. Beyond NPS 8, however, there are two different versions of schedules 5, 10, 40, and 80. In newer standards and in the table below, the distinction is denoted by the presence or absence of an 'S' suffix after the schedule number. The 'S' was originally meant to indicate Stainless Steel Schedule (Ref. #3, pp B-16 and B-17), but in practice, pipe of any material may be available in either schedule depending on the manufacturer.
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.
Copper plumbing tube for residential plumbing follows an entirely different size system; see domestic water system. Both polyvinyl chloride pipe (PVC) and chlorinated polyvinyl chloride pipe (CPVC) are made in NPS sizes. CPVC has a roughly 50°C higher temperature limit which makes it suitable for use in domestic hot water service.
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[edit] NPS 1/8 to NPS 3-1/2
| NPS | DN | OD (inches) | Wall Thickness (inches) | ||||||
|---|---|---|---|---|---|---|---|---|---|
| SCH 5 | SCH 10 | SCH 30 | SCH 40 | SCH 80 | SCH 120 | SCH 160 | |||
| 1/8 | 6 | 0.405 | 0.035 | 0.049 | 0.057 | 0.068 | 0.095 | ? | ? |
| 3/16 | 7 | ? | ? | ? | ? | ? | ? | ? | ? |
| 1/4 | 8 | 0.540 | 0.049 | 0.065 | .073 | .088 | .119 | ? | ? |
| 3/8 | 10 | 0.675 | .049 | .065 | .073 | .091 | .126 | ? | ? |
| 1/2 | 15 | 0.840 | .065 | .083 | .095 | .109 | .147 | .170 | .188 |
| 5/8 | 18 | ? | ? | ? | ? | ? | ? | ? | ? |
| 3/4 | 20 | 1.050 | .065 | .083 | .095 | .113 | .154 | .170 | .219 |
| 1 | 25 | 1.315 | .065 | .109 | .114 | .133 | .179 | .200 | .250 |
| 1-1/4 | 32 | 1.660 | .065 | .109 | .117 | .140 | .191 | .215 | .250 |
| 1-1/2 | 40 | 1.900 | .065 | .109 | .125 | .145 | .200 | .225 | .281 |
| 2 | 50 | 2.375 | .065 | .109 | ? | .154 | .218 | .250 | .344 |
| 2-1/2 | 65 | 2.875 | .083 | .120 | ? | .203 | .276 | .300 | .375 |
| 3 | 80 | 3.500 | .083 | .120 | ? | .216 | .300 | .350 | .438 |
| 3-1/2 | 90 | 4.000 | .083 | .120 | ? | .226 | .318 | ? | ? |
[edit] NPS 4 to NPS 9
| NPS | DN | OD (inches) | Wall Thickness (inches) | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| SCH 5 | SCH 10 | SCH 20 | SCH 30 | SCH 40/STD | SCH 60 | SCH 80 | SCH 100 | SCH 120 | SCH 140 | SCH 160 | |||
| 4 | 100 | 4.500 | .083 | .120 | ? | ? | .237 | .281 | .337 | ? | .437 | ? | .531 |
| 4-1/2 | 115 | 5.000 | ? | ? | ? | ? | .247 | ? | .355 | ? | ? | ? | ? |
| 5 | 125 | 5.563 | .109 | .134 | ? | ? | .258 | ? | .375 | ? | .500 | ? | .625 |
| 6 | 150 | 6.625 | .109 | .134 | ? | ? | .280 | ? | .432 | ? | .562 | ? | .719 |
| 7 | 175 | 7.625 | ? | ? | ? | ? | .301 | ? | .500 | ? | ? | ? | .857 |
| 8 | 200 | 8.625 | .109 | .148 | .250 | .277 | .322 | .406 | .500 | .593 | .718 | .812 | .906 |
| 9 | 225 | 9.625 | ? | ? | ? | ? | .342 | ? | .500 | ? | ? | ? | ? |
[edit] NPS 10 to NPS 24
| NPS | DN | OD (inches) | Wall Thickness (inches) | ||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| SCH 5s | SCH 5 | SCH 10s | SCH 10 | SCH 20 | SCH 30 | SCH 40s | SCH 40 | SCH 60 | SCH 80s | SCH 80 | SCH 100 | SCH 120 | SCH 140 | SCH 160 | |||
| 10 | 250 | 10.75 | .134 | .134 | .165 | .165 | .250 | .307 | .365 | .365 | .500 | .500 | .593 | .718 | .843 | 1.000 | 1.125 |
| 12 | 300 | 12.75 | .156 | .165 | .180 | .180 | .250 | .330 | .375 | .406 | .500 | .500 | .687 | .843 | 1.000 | 1.125 | 1.312 |
| 14 | 350 | 14.00 | .156 | .188 | .250 | .312 | .375 | .375 | .437 | .593 | .500 | .750 | .937 | 1.093 | 1.250 | 1.406 | |
| 16 | 400 | 16.00 | .165 | .188 | .250 | .312 | .375 | .375 | .500 | .656 | .500 | .843 | 1.031 | 1.218 | 1.437 | 1.593 | |
| 18 | 450 | 18.00 | .165 | .188 | .250 | .312 | .437 | .375 | .562 | .750 | .500 | .937 | 1.156 | 1.375 | 1.562 | 1.781 | |
| 20 | 500 | 20.00 | .188 | .218 | .250 | .375 | .500 | .375 | .593 | .812 | .500 | 1.031 | 1.280 | 1.500 | 1.750 | 1.968 | |
| 24 | 600 | 24.00 | .218 | .250 | .250 | .375 | .562 | .375 | .687 | .968 | .500 | 1.218 | 1.531 | 1.812 | 2.062 | 2.343 | |
[edit] See also
[edit] References
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This article or section includes a list of references or external links, but its sources remain unclear because it lacks in-text citations. You can improve this article by introducing more precise citations. |
- Oberg, Erik; Franklin D. Jones, Holbrook L. Horton, and Henry H. Ryffel (2000). in ed. Christopher J. McCauley, Riccardo Heald, and Muhammed Iqbal Hussain: Machinery's Handbook, 26th Edition, 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, 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, Joliet, IL: Crane Co..
- ANSI/ASME Standard 36.19M - Stainless Steel Pipe.
- ANSI/ASTM Reference R0036 - Stainless Steel Pipe.
