NPS vs. DN and Class vs. PN

Because in the piping and process industry, most advanced and pioneering technologies are developed by companies originated in US, the piping nomenclature has been heavily influenced by imperial system. In this system, pounds per square inch(psi) is used to refer to pressure while nominal pipe size(NPS) is used to refer to size of pipe. However there is also another very important nomenclature system: metric system, which was established by the International Standards Organization(ISO). The basic unit to describe length or size is meter in metric system with an extension ofmillimeter and centimeter, etc. It also refers to the pipe diameters as nominal diameter(DN) and pressure ratings asnominal pressure(PN). Pressures are noted in kilopascal(kPa) or bar.

1. Nominal Pipe Size(NPS) & Nominal Diameter(DN) Comparison Table

Nominal Pipe Size(NPS) inches	Nominal Diameter(DN) millimeters
1/4"	6
1/2"	15
3/4"	20
1"	25
1-1/4"	32
1-1/2"	40
2"	50
2-1/2"	65
3"	80
4"	100
5"	125
6"	150
8"	200
10"	250
12"	300
14"	350
16"	400
18"	450
20"	500
24"	600

2. ASME Pressure Class & ISO Nominal Pressure

ASME Pressure Class psi	Nominal Pressure(PN) bar
150	16
300	40
400	64
600	100
900	160
1500	250
2500	400
4500	700

*Note: PN is an approximation to the corresponding ASME pressure class, and should not

be used as an exact correlation between the two standards. PN correlate to EN

DIN/BS pressure-temperature rating standards, which may vary significantly from

ASME pressure-temperature ratings.

Views: Author：hbmetals Date:15/07/13