Home » Introduction » Nominal Pipe Size NPS, Nominal Bore NB, Outside Diameter OD

Nominal Pipe Size NPS, Nominal Bore NB, Outside Diameter OD

What is a relation between NPS, NB & OD of a pipe?

What is NPT & what are its applications?

What is a relation between NPS, NB & OD of a pipe?

Nominal Pipe Size (NPS) is a North American set of standard sizes for pipes used for high or low pressures and temperatures. Pipe size is specified with two non-dimensional numbers: a nominal pipe size (NPS) for diameter based on inches, and a schedule (Sched. or Sch.) for wall thickness. NPS is often incorrectly called National Pipe Size, due to confusion with national pipe thread (NPT)

NB (nominal bore) is the European designation equivalent to NPS is DN (diamètre nominal/nominal diameter/Durchmesser nach Norm), in which sizes are measured in millimeters. NB (nominal bore) is also frequently used interchangeably with NPS.

OD is the outside diameter of the pipe and is fixed for a given size.




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. 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.

For NPS of 5 and larger, the DN is equal to the NPS multiplied by 25 (not 25.4).

Table below shows the relation between Nominal pipe size, Nominal diameter & outside diameter for pipes:

Nominal Pipe size
NPS
[inches]
Nominal Diameter
DN
[mm]
Outside Diameter
OD
[mm]

1/2

15

21.3

3/4

20

26.7

1

25

33.4

1 1/4

32

42.16

1 1/2

40

48.26

2

50

60.3

2 1/2

65

73.03

3

80

88.9

4

100

114.3

5

125

141.3

6

150

168.28

8

200

219.08

10

250

273.05

12

300

323.85

14

350

355.6

16

400

406.4

18

450

457.2

20

500

508

24

600

609.6

28

700

711.2

32

800

812.8

36

900

914.4

40

1000

1016

42

1050

1066.8

44

1100

1117.6

48

1200

1219.2

52

1300

1320.8

56

1400

1422.4

60

1500

1524

64

1600

1625.6

68

1700

1727.2

72

1800

1828.8

76

1900

1930.4

80

2000

2032

88

2200

2235.2

96

2400

2438.4

104

2600

2641.6

112

2800

2844.8

120

3000

3048

128

3200

3251.2

 

What is NPT & what are its applications?

NPT is the abbreviation used for National Pipe Thread Taper. It is an American National Standard used to join pipes & fittings. ASME B1.20.1 is the standard used for NPT which covers dimensions and gaging of pipe threads for general purpose.

Most commonly used sizes for pipes & fittings by the U.S. suppliers commonly are 1/8, 1/4, 3/8, 1/2, 3/4, 1, 1 ¼, 1 ½ and 2 inch. Smaller sizes than those listed are occasionally used for compressed air. For sizes larger than 3 inches and above there are other method of joining available so threading is less frequently used in this sizes.

Sometimes NPT threads are referred to as MPT (Male Pipe Thread), MNPT, or NPT (M) for male (external) threads and FPT (Female Pipe Thread), FNPT, or NPT (F) for female (internal) threads.

For details on NPT, refer to clause 3 of ASME B1.20.1- SPECIFICATION FOR GENERAL PURPOSE TAPER PIPE THREADS, NPT

American national standard taper thread notation

Fig 3 American national standard taper thread notation

Click to enlarge the table

Basic dimensions american national standard taper thread

Basic dimensions american national standard taper thread- Table 1

Click to enlarge the table

Basic dimensions american national standard taper thread

Basic dimensions american national standard taper thread – Table 2

Add Comment Register



Leave a Reply

Your email address will not be published. Required fields are marked *

*

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>