PN or Pressure Nominal is the value in bars indicating the maximum pressure that the HDPE pipe can withstand without failure. PN or Pressure Nominal for HDPE pipe is designed from PN 3.2 bar where it can withstand pressure of 3.2 bars up to PN 25 where it can withstand pressure of 25 bars. Pipe thickness increases with the increase in PN value.
Higher PN or Pressure Nominal should be selected when designing the use of HDPE pipe at high pressure for safety and durability of the pipe.
How to calculate PN?
The relationship between nominal pressure, PN, design stress, σs, and the series S/SDR is given by the following equation:
PN = \( \frac{10\sigma_{s}}{S} \) or PN = \( \frac{20\sigma_{s}}{SDR-1} \)
where \[\sigma_{s} = \frac{\boldsymbol{MRS}}{\mathbf{C}} \] and C = 1.25.
Examples of the relationship between PN, MRS, S and SDR at 20 °C (C = 1,25)
| SDR | S | Nominal pressure for material class bar | |||
|---|---|---|---|---|---|
| PE 40 | PE 63 | PE 80 | PE 100 | ||
| 41 | 20 | – | 2,5 | 3,2 | 4 |
| 33 | 16 | – | 3,2 | 4 | 5 |
| 26 | 12,5 | 2,5 | 4 | 5 | 6a |
| 21 | 10 | 3,2 | 5 | 6a | 8 |
| 17 | 8 | 4 | 6a | 8 | 10 |
| 13,6 | 6,3 | 5 | 8 | 10 | 12,5 |
| 11 | 5 | – | 10 | 12,5 | 16 |
| 9 | 4 | 8 | – | 16 | 20 |
| 7,4 | 3,2 | 10 | – | 20 | 25 |
| 6 | 2,5 | – | – | 25 | – |
| NOTE: 1 bar = 0,1 Mpa = 105 pa; 1 Mpa = N/mm2. | |||||
| a Actual calculated values are 6,4 bar for PE 100 and 6,3 bar for PE 80 and PE 63. | |||||
ISO4427-2: Plastics piping systems — Polyethylene (PE) pipes and fittings for water supply — Part 2: Pipes.
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