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

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