Nominal Pipe Size
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2008-07-09T15:04:11Z
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'''Nominal Pipe Size''' (NPS) is a North American set of standard sizes for pipes used for high or low pressures and temperatures.<ref name = "B36.10M-p-1">ASME B36.10M-2004, p. 1</ref> Pipe size is specified with two non-dimensional numbers: a Nominal Pipe Size (NPS) based on inches, and a Schedule (Sch). NPS is often incorrectly called National Pipe Size, due to confusion with [[National Pipe Thread]]. For other pipe size standards, see [[Pipe (material)#Sizes|Pipe (material) - Sizes]]. The European designation equivalent to NPS is DN (Diametre Nominel), which is based on millimetres.<ref>[http://www.engineeringtoolbox.com/nps-nominal-pipe-sizes-d_45.html NPS - "Nominal Pipe Size" and DN - "Diametre Nominal"], EngineeringToolbox.com</ref>
==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|Iron pipe size (IPS)]] system of the day. However these three sizes did not fit all applications. The committee surveyed industry and created a system of Schedule Numbers that designated wall thicknesses based on smaller steps between sizes,<ref name="B36.10M-p-iv">ASME B36.10M-2004, p. iv</ref> 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.<ref name="B36.10M-p-iv"/><ref name = "piping_handbook"/> 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, ''and'' Double Extra-Heavy'', 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 [[American Petroleum Institute|API]], [[ASTM International|ASTM]], and others.<ref name="B36.10M-p-iv"/>
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 [[Stubs Iron Wire Gauge|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.<ref>ASME Standard 36.19M-2004, p. iv</ref>
==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 36.19M. 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 (material)|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.<ref name = "piping_handbook">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.]</ref>
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.<ref name = "B36.10M-p-1"/>
Both [[Polyvinyl chloride|polyvinyl chloride]] pipe (PVC) and [[Chlorinated polyvinyl chloride|chlorinated polyvinyl chloride]] pipe (CPVC) are made in NPS sizes.
==NPS tables for selected sizes==
=== NPS ⅛ to NPS 3½ ===
<TABLE border="1">
<TR><TH rowspan="2">NPS<TH rowspan="2">DN<TH rowspan="2">OD (inches)<TH colspan="7">Wall Thickness (inches)
<TR> <TH>SCH 5<TH>SCH 10<TH>SCH 30<TH>SCH 40<TH>SCH 80<TH>SCH 120<TH>SCH 160
<TR><TH>⅛ <TH>6 <TD>0.405<TD>0.035 <TD>0.049 <TD>0.057 <TD>0.068 <TD>0.095 <TD>--- <TD>---
<TR><TH>¼ <TH>8 <TD>0.540<TD>0.049 <TD>0.065 <TD>.073 <TD>.088 <TD>.119 <TD>--- <TD>---
<TR><TH>⅜ <TH>10 <TD>0.675<TD>.049 <TD>.065 <TD>.073 <TD>.091 <TD>.126 <TD>--- <TD>---
<TR><TH>½ <TH>15 <TD>0.840<TD>.065 <TD>.083 <TD>.095 <TD>.109 <TD>.147 <TD>.170 <TD>.188
<TR><TH>¾ <TH>20 <TD>1.050<TD>.065 <TD>.083 <TD>.095 <TD>.113 <TD>.154 <TD>--- <TD>.219
<TR><TH>1 <TH>25 <TD>1.315<TD>.065 <TD>.109 <TD>.114 <TD>.133 <TD>.179 <TD>--- <TD>.250
<TR><TH>1¼ <TH>32 <TD>1.660<TD>.065 <TD>.109 <TD>.117 <TD>.140 <TD>.191 <TD>--- <TD>.250
<TR><TH>1½ <TH>40 <TD>1.900<TD>.065 <TD>.109 <TD>.125 <TD>.145 <TD>.200 <TD>--- <TD>.281
<TR><TH>2 <TH>50 <TD>2.375<TD>.065 <TD>.109 <TD>.125 <TD>.154 <TD>.218 <TD>.250 <TD>.344
<TR><TH>2½ <TH>65 <TD>2.875<TD>.083 <TD>.120 <TD>.188 <TD>.203 <TD>.276 <TD>.300 <TD>.375
<TR><TH>3 <TH>80 <TD>3.500<TD>.083 <TD>.120 <TD>.188 <TD>.216 <TD>.300 <TD>.350 <TD>.438
<TR><TH>3½ <TH>90 <TD>4.000<TD>.083 <TD>.120 <TD>.188 <TD>.226 <TD>.318 <TD>--- <TD>---
</TABLE>
=== NPS 4 to NPS 9 ===
<TABLE border="1">
<TR><TH rowspan="2">NPS<TH rowspan="2">DN<TH rowspan="2">OD (inches)<TH colspan="11">Wall Thickness (inches)
<TR> <TH>SCH 5<TH>SCH 10<TH>SCH 20<TH>SCH 30<TH>SCH 40/STD<TH>SCH 60<TH>SCH 80<TH>SCH 100<TH>SCH 120<TH>SCH 140<TH>SCH 160
<TR><TH>4 <TH>100<TD>4.500<TD>.083<TD>.120<TD>--- <TD>.188 <TD>.237 <TD>.281 <TD>.337 <TD>--- <TD>.437 <TD>--- <TD>.531
<TR><TH>4½ <TH>115<TD>5.000 <TD>--- <TD>--- <TD>--- <TD>--- <TD>.247 <TD>--- <TD>.355 <TD>--- <TD>--- <TD>--- <TD>---
<TR><TH>5 <TH>125<TD>5.563<TD>.109<TD>.134<TD>--- <TD>--- <TD>.258 <TD>--- <TD>.375 <TD>--- <TD>.500 <TD>--- <TD>.625
<TR><TH>6 <TH>150<TD>6.625<TD>.109<TD>.134<TD>--- <TD>--- <TD>.280 <TD>--- <TD>.432 <TD>--- <TD>.562 <TD>--- <TD>.719
<TR><TH>8 <TH>200<TD>8.625<TD>.109<TD>.148<TD>.250 <TD>.277 <TD>.322 <TD>.406 <TD>.500 <TD>.593 <TD>.718 <TD>.812 <TD>.906
</TABLE>
=== NPS 10 to NPS 24 ===
<TABLE border="1">
<TR><TH rowspan="2">NPS<TH rowspan="2">DN<TH rowspan="2">OD (inches)<TH colspan="15">Wall Thickness (inches)
<TR> <TH>SCH 5s<TH>SCH 5<TH>SCH 10s<TH>SCH 10<TH>SCH 20<TH>SCH 30<TH>SCH 40s<TH>SCH 40<TH>SCH 60<TH>SCH 80s<TH>SCH 80<TH>SCH 100<TH>SCH 120<TH>SCH 140<TH>SCH 160
<TR><TH>10<TH>250<TD>10.75<TD>.134 <TD>.134 <TD>.165 <TD>.165 <TD>.250 <TD>.307 <TD>.365 <TD>.365 <TD>.500 <TD>.500 <TD>.593 <TD>.718 <TD>.843 <TD>1.000 <TD>1.125
<TR><TH>12<TH>300<TD>12.75<TD>.156 <TD>.165 <TD>.180 <TD>.180 <TD>.250 <TD>.330 <TD>.375 <TD>.406 <TD>.500 <TD>.500 <TD>.687 <TD>.843 <TD>1.000 <TD>1.125 <TD>1.312
<TR><TH>14<TH>350<TD>14.00<TD>.156 <TD>.156 <TD>.188 <TD>.250 <TD>.312 <TD>.375 <TD>.375 <TD>.437 <TD>.593 <TD>.500 <TD>.750 <TD>.937 <TD>1.093 <TD>1.250 <TD>1.406
<TR><TH>16<TH>400<TD>16.00<TD>.165 <TD>.165 <TD>.188 <TD>.250 <TD>.312 <TD>.375 <TD>.375 <TD>.500 <TD>.656 <TD>.500 <TD>.843 <TD>1.031 <TD>1.218 <TD>1.437 <TD>1.593
<TR><TH>18<TH>450<TD>18.00<TD>.165 <TD>.165 <TD>.188 <TD>.250 <TD>.312 <TD>.437 <TD>.375 <TD>.562 <TD>.750 <TD>.500 <TD>.937 <TD>1.156 <TD>1.375 <TD>1.562 <TD>1.781
<TR><TH>20<TH>500<TD>20.00<TD>.188 <TD>.188 <TD>.218 <TD>.250 <TD>.375 <TD>.500 <TD>.375 <TD>.593 <TD>.812 <TD>.500 <TD>1.031 <TD>1.280 <TD>1.500 <TD>1.750 <TD>1.968
<TR><TH>24<TH>600<TD>24.00<TD>.218 <TD>.218 <TD>.250 <TD>.250 <TD>.375 <TD>.562 <TD>.375 <TD>.687 <TD>.968 <TD>.500 <TD>1.218 <TD>1.531 <TD>1.812 <TD>2.062 <TD>2.343
</TABLE>
''Note: --- = size not designated.
== See also ==
* [[British standard pipe|British standard pipe sizes]]
* [[British standard pipe thread|British standard pipe thread sizes]]
== Sources ==
*{{cite book
| first = Erik
| last = Oberg
| coauthors = Franklin D. Jones, Holbrook L. Horton, and Henry H. Ryffel
| year = 2000
| title = '''[[Machinery's Handbook]]'''
| editor = ed. Christopher J. McCauley, Riccardo Heald, and Muhammed Iqbal Hussain
| edition = 26th Edition
| publisher = Industrial Press Inc.
| location = New York
| id = ISBN 0-8311-2635-3
}}
*{{cite book
| first = Mohinder L.
| last = Nayyar, P.E.
| year = 2000
| title = '''Piping Handbook'''
| chapter = A1
| editor = Mohinder L. Nayyar, P.E.
| edition = 7th
| publisher = McGraw-Hill
| location = New York
| id = ISBN 0-07-047106-1
}}
*{{cite book
| last = Engineering Department
| year = 1988
| title = '''Flow of Fluids Through Valves, Fittings, and Pipe (Technical Paper No. 410)'''
| edition = 25th Printing—1991
| publisher = Crane Co.
| location = Joliet, IL
}}
*{{cite book
| title = '''ASME B36.10M - Welded and Seamless Wrought Steel Pipe'''
}}
*{{cite book
| title = '''ANSI/ASME Standard 36.19M - Stainless Steel Pipe'''
}}
*{{cite book
| title = '''ANSI/ASTM Reference R0036 - Stainless Steel Pipe'''
}}
* [http://www.engineersedge.com/pipe_schedules.htm Table of Pipe Schedules] from EngineersEdge.com.
== References ==
<references/>
[[Category:Piping]]
[[Category:Mechanical standards]]
[[de:Nennweite]]
[[eo:Nominal Pipe Size]]
[[pt:Diâmetro nominal]]