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.
Among the calculators for the plastics maker programme you will find «PE-rør: trykklasse (SDR/PN)» (PE pipe: pressure class). It works it out for you.
Ground-source heat collectors are PE pipes in the ground. The chart shows how many buildings in each municipality have ground-source heating.