Reading PE Pipe Markings: SDR, Pressure Rating and Safety Factor
Every metre of PE pipe carries a print line. It is applied during extrusion, it repeats every metre or so, and it is the cheapest quality-control instrument on the whole project. Yet in most disputes about a delivery, nobody reads it until the pipe is already in the trench.
A typical line looks like this:
PE100 · DN315 · SDR17 · PN10 · EN 12201-2 · 18.5 mm · 2026-09 · BATCH 260914-07
Seven pieces of information, each answering a different question.
Grade, then size
PE100 is the material grade. DN315 is the nominal outside diameter in millimetres — for PE pressure pipe, DN is always the outside diameter, never the bore. That single convention explains most of the confusion when a buyer compares a PE pipe with a steel or cast-iron pipe of the same nominal size: the PE pipe carries a noticeably larger bore, because the wall is thinner than a metal pipe of equivalent pressure class.
SDR is a ratio, not a class
Standard dimension ratio is outside diameter divided by wall thickness. SDR17 on DN315 means 315 / 17 = 18.5 mm. The ratio is fixed by the standard, so once you know SDR and diameter, the wall is determined — there is no such thing as a thick SDR17.
| SDR | Wall at DN110 | Wall at DN315 | PN, PE100 |
|---|---|---|---|
| SDR26 | 4.2 mm | 12.1 mm | PN 6 |
| SDR21 | 5.3 mm | 15.0 mm | PN 8 |
| SDR17 | 6.6 mm | 18.7 mm | PN 10 |
| SDR13.6 | 8.1 mm | 23.2 mm | PN 12.5 |
| SDR11 | 10.0 mm | 28.6 mm | PN 16 |
Note that wall thickness is not rounded to a convenient number. It is calculated, then rounded according to the tolerance rules in the standard, which is why a table and a caliper reading can differ by a few tenths of a millimetre and both be correct.
The safety factor is already inside the number
PN is not burst pressure and it is not the pressure at which the pipe was tested at the factory. It is the permissible working pressure for fifty years at 20 °C, derived from design stress divided by the geometry. For PE100 at SDR17: 2 × 8.0 / 16 = 1.0 MPa, hence PN10. The factor of 1.25 (or 1.6 for gas) has already been applied, and so has the fifty-year extrapolation.
Designers sometimes add a second safety factor on top of PN. That is legitimate, but it should be a deliberate decision written into the calculation, not a reflex that doubles the wall thickness and the budget.
Three markings that get misread
- PN vs SDR. Two pipes with the same PN but different SDR are not interchangeable. PN10 at SDR17 and PN10 at SDR13.6 are different products for different duty.
- Batch and date. The batch code ties the coil to a test report. If the report you were sent does not carry the same batch, it is not evidence about your pipe.
- Standard number. EN 12201, ISO 4427, ASTM F714 and GB/T 13663 all define PE pressure pipe, but they do not define identical tolerances or test frequencies. The standard on the print line must be the one in your purchase order.
What the marking cannot tell you
It cannot tell you whether the compound was dry when it went into the hopper, whether the die was clean, or whether the coil was stored in the sun for a season. Those show up as surface roughness, ovality, or a wall that tapers by half a millimetre over six metres. A print line confirms identity; it does not confirm workmanship. Both checks belong at goods-in.
If you need help matching a duty point to a diameter, SDR and grade, send us the flow, the working pressure, the burial depth and the soil type, and we will return the calculation with the marking line you should expect to see on the pipe. HDPE water pipe specifications.
