What is the difference between Inch, DN, PN and Class?
2020/09/27 16:18:46
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.
Nominal Pipe Size(NPS) & Nominal Diameter(DN) Comparison Table
| Nominal Pipe Size(NPS) | Nominal Diameter(DN) |
| inches | 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 |
ASME Pressure Class & ISO Nominal Pressure
| ASME Pressure Class | Nominal Pressure(PN) |
| psi | 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.
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