SDR, PN and pressure: reading a PE pipe
From diameter and wall thickness to pressure in bar
Introduction
SDR stands for Standard Dimension Ratio. It is the pipe's outside diameter divided by the wall thickness. A pipe with a diameter (d) of 110 mm and a wall thickness (e) of 10 mm is therefore SDR 11. The larger the SDR, the thinner the wall relative to the diameter.
From SDR to pressure
The PE100+ Association, an association of pipe manufacturers, uses this formula for the maximum operating pressure (MOP) in a water pipe: pressure (bar) = 20 · MRS ÷ (C · (SDR − 1)). MRS is the strength of the material. For PE 100 it is 10 MPa. C is the safety factor. For water it is at least 1.25.
| SDR (standard dimension ratio) | Calculation (PE 100, C = 1.25) | Maximum operating pressure |
|---|---|---|
| 11 | PN = 20 · 10 ÷ (1.25 · 10) | 16 bar (pressure) |
| 17 | PN = 20 · 10 ÷ (1.25 · 16) | 10 bar (pressure) |
| 26 | PN = 20 · 10 ÷ (1.25 · 25) | 6.4 bar |
The result is called the pipe's pressure class and is often written as PN, e.g. PN 16. Note that the pressure falls as SDR rises.
Ground-source heat collectors are PE pipes in the ground. The chart shows how many buildings in each municipality have ground-source heating.