Most municipal water specifications arrive as a drawing with a diameter and a pressure, and a tender document that says “PE100 to ISO 4427”. The diameter is settled. The SDR is where the arguments start, because it decides the wall, the weight per metre, the price and — on a long line — the flow.
Step 1: establish the real working pressure
Static head from the reservoir or tower is only part of it. Add pump shut-off head if the line is pumped, and add surge. A line that sits at 6 bar in steady state can see 10 bar for a second when a valve closes.
| Condition | What it adds | Practical effect |
|---|---|---|
| Static head only | Gravity from the highest point | PN10 usually enough |
| Pumped line, steady state | Pump curve at duty point | PN10 or PN12.5 |
| Pumped line with valve closure | Surge, often 1.5–2× steady | PN16, or add an air valve |
Rule we quote by: specify one class above the calculated steady-state pressure unless surge has been modelled. The extra wall is cheaper than the repair.
Step 2: choose the SDR that delivers that class
For PE100 water pipe: SDR26 = PN6, SDR17 = PN10, SDR13.6 = PN12.5, SDR11 = PN16, SDR9 = PN20, SDR7.4 = PN25. A PN16 line means SDR11 — which is roughly 55 % heavier per metre than SDR17 at the same diameter. That difference is what the freight and the lifting plan see.
Step 3: decide coil or straight
- Coil to DN110 — fewer joints, faster laying, good for distribution and service lines.
- Straight 6 m / 12 m above DN160 — coils become too stiff to handle without a decoiler.
- Joints cost money: every butt-fusion joint is machine time, an operator and a fusion record. A coiled 500 m run has none of those.
Step 4: jointing and fittings
Butt fusion for main-line joints, electrofusion for tie-ins and repairs, flanged transitions at pumps, valves and meters. The fittings must match the pipe SDR — a PN16 fitting on a PN10 pipe is a wasted upgrade, and the reverse is a weak point.
Step 5: what belongs in the quotation
- The standard (ISO 4427-2 / EN 12201-2) and the SDR per diameter
- Wall thickness and mass per metre, so freight can be calculated
- Fittings list with counts, matched to the drawing
- Loading plan: how many metres per container at your diameters
- Test reports and mill certificate, before the balance is paid
Common specification mistakes
- PN quoted at 20 °C for a line that runs at 40 °C — allowable pressure drops; derate before choosing SDR.
- Mixing SDR in one line — allowed at fittings, but the weakest section sets the rating for the whole run.
- Ignoring burial depth — deep cover needs either a thicker wall or a proper bedding design; PE is flexible, not indestructible.
- No spare couplings — the first excavator strike happens on a Friday.
Send the drawing, the pump curve and the destination port. We return the SDR per diameter, the fitting list and the loading plan in one document.